Re-architect formatting to prepare for cohosting (and for fun!) (#10778)

I nerd sniped myself thinking about how to get formatting into
cohosting, given the limitations Alex ran into doing the relayering for
auto insert, and this is the result. I was going to go further and port
the actual formatting endpoint to cohosting, but that would have ran
into the same issue that Alex did with auto insert, so I figured I'd
wait for that to merge, and put this up in the meantime.

This unblocks the formatting, code action and completion end points from
being ported.
Part of #10743
Part of #9519

I **strongly** recommend reviewing commit-at-a-time, as I did this
deliberately in an order, and in order to (hopefully) make reviewing
easier. Though granted, there are a lot of commits.

src/Razor/benchmarks/Microsoft.AspNetCore.Razor.Microbenchmarks/LanguageServer/RazorCSharpFormattingBenchmark.cs

@@ -110,15 +110,9 @@ void Method() { }
     [Benchmark(Description = "Formatting")]
     public async Task RazorCSharpFormattingAsync()
     {
-        var options = new FormattingOptions()
-        {
-            TabSize = 4,
-            InsertSpaces = true
-        };
-
         var documentContext = new DocumentContext(DocumentUri, DocumentSnapshot, projectContext: null);
 
-        var edits = await RazorFormattingService.FormatAsync(documentContext, range: null, options, CancellationToken.None);
+        var edits = await RazorFormattingService.GetDocumentFormattingEditsAsync(documentContext, htmlEdits: [], range: null, RazorFormattingOptions.Default, CancellationToken.None);
 
 #if DEBUG
         // For debugging purposes only.

src/Razor/src/Microsoft.AspNetCore.Razor.LanguageServer/AutoInsert/OnAutoInsertEndpoint.cs

@@ -4,7 +4,7 @@
 using System;
 using System.Collections.Frozen;
 using System.Collections.Generic;
-using System.Collections.Immutable;
+using System.Diagnostics;
 using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
@@ -185,19 +185,21 @@ public void ApplyCapabilities(VSInternalServerCapabilities serverCapabilities, V
         }
 
         // For C# we run the edit through our formatting engine
-        var edits = new[] { delegatedResponse.TextEdit };
+        Debug.Assert(positionInfo.LanguageKind == RazorLanguageKind.CSharp);
 
-        var mappedEdits = delegatedResponse.TextEditFormat == InsertTextFormat.Snippet
-            ? await _razorFormattingService.FormatSnippetAsync(documentContext, positionInfo.LanguageKind, edits, originalRequest.Options, cancellationToken).ConfigureAwait(false)
-            : await _razorFormattingService.FormatOnTypeAsync(documentContext, positionInfo.LanguageKind, edits, originalRequest.Options, hostDocumentIndex: 0, triggerCharacter: '\0', cancellationToken).ConfigureAwait(false);
-        if (mappedEdits is not [{ } edit])
+        var options = RazorFormattingOptions.From(originalRequest.Options, _optionsMonitor.CurrentValue.CodeBlockBraceOnNextLine);
+
+        var mappedEdit = delegatedResponse.TextEditFormat == InsertTextFormat.Snippet
+            ? await _razorFormattingService.GetCSharpSnippetFormattingEditAsync(documentContext, [delegatedResponse.TextEdit], options, cancellationToken).ConfigureAwait(false)
+            : await _razorFormattingService.GetSingleCSharpEditAsync(documentContext, delegatedResponse.TextEdit, options, cancellationToken).ConfigureAwait(false);
+        if (mappedEdit is null)
         {
             return null;
         }
 
         return new VSInternalDocumentOnAutoInsertResponseItem()
         {
-            TextEdit = edit,
+            TextEdit = mappedEdit,
             TextEditFormat = delegatedResponse.TextEditFormat,
         };
     }

src/Razor/src/Microsoft.AspNetCore.Razor.LanguageServer/CodeActions/CSharp/DefaultCSharpCodeActionResolver.cs

@@ -22,21 +22,6 @@ internal sealed class DefaultCSharpCodeActionResolver(
     IClientConnection clientConnection,
     IRazorFormattingService razorFormattingService) : CSharpCodeActionResolver(clientConnection)
 {
-    // Usually when we need to format code, we utilize the formatting options provided
-    // by the platform. However, we aren't provided such options in the case of code actions
-    // so we use a default (and commonly used) configuration.
-    private static readonly FormattingOptions s_defaultFormattingOptions = new FormattingOptions()
-    {
-        TabSize = 4,
-        InsertSpaces = true,
-        OtherOptions = new Dictionary<string, object>
-        {
-            { "trimTrailingWhitespace", true },
-            { "insertFinalNewline", true },
-            { "trimFinalNewlines", true },
-        },
-    };
-
     private readonly IDocumentContextFactory _documentContextFactory = documentContextFactory;
     private readonly IRazorFormattingService _razorFormattingService = razorFormattingService;
 
@@ -80,11 +65,10 @@ public async override Task<CodeAction> ResolveAsync(
 
         // Remaps the text edits from the generated C# to the razor file,
         // as well as applying appropriate formatting.
-        var formattedEdits = await _razorFormattingService.FormatCodeActionAsync(
+        var formattedEdit = await _razorFormattingService.GetCSharpCodeActionEditAsync(
             documentContext,
-            RazorLanguageKind.CSharp,
             csharpTextEdits,
-            s_defaultFormattingOptions,
+            RazorFormattingOptions.Default,
             cancellationToken).ConfigureAwait(false);
 
         cancellationToken.ThrowIfCancellationRequested();
@@ -99,7 +83,7 @@ public async override Task<CodeAction> ResolveAsync(
                 new TextDocumentEdit()
                 {
                     TextDocument = codeDocumentIdentifier,
-                    Edits = formattedEdits,
+                    Edits = formattedEdit is null ? [] : [formattedEdit],
                 }
             }
         };

src/Razor/src/Microsoft.AspNetCore.Razor.LanguageServer/CodeActions/CSharp/TypeAccessibilityCodeActionProvider.cs

@@ -16,6 +16,7 @@
 using Microsoft.AspNetCore.Razor.PooledObjects;
 using Microsoft.AspNetCore.Razor.Threading;
 using Microsoft.CodeAnalysis.ExternalAccess.Razor;
+using Microsoft.CodeAnalysis.Razor.Formatting;
 using Microsoft.CodeAnalysis.Text;
 using Microsoft.VisualStudio.LanguageServer.Protocol;
 
@@ -138,7 +139,7 @@ private static ImmutableArray<RazorVSInternalCodeAction> ProcessCodeActionsVSCod
                 var fqnCodeAction = CreateFQNCodeAction(context, diagnostic, codeAction, fqn);
                 typeAccessibilityCodeActions.Add(fqnCodeAction);
 
-                if (AddUsingsCodeActionProviderHelper.TryCreateAddUsingResolutionParams(fqn, context.Request.TextDocument.Uri, additionalEdit: null, out var @namespace, out var resolutionParams))
+                if (AddUsingsCodeActionResolver.TryCreateAddUsingResolutionParams(fqn, context.Request.TextDocument.Uri, additionalEdit: null, out var @namespace, out var resolutionParams))
                 {
                     var addUsingCodeAction = RazorCodeActionFactory.CreateAddComponentUsing(@namespace, newTagName: null, resolutionParams);
                     typeAccessibilityCodeActions.Add(addUsingCodeAction);
@@ -191,7 +192,7 @@ private static ImmutableArray<RazorVSInternalCodeAction> ProcessCodeActionsVS(
             // For add using suggestions, the code action title is of the form:
             // `using System.Net;`
             else if (codeAction.Name is not null && codeAction.Name.Equals(RazorPredefinedCodeFixProviderNames.AddImport, StringComparison.Ordinal) &&
-                AddUsingsCodeActionProviderHelper.TryExtractNamespace(codeAction.Title, out var @namespace, out var prefix))
+                AddUsingsHelper.TryExtractNamespace(codeAction.Title, out var @namespace, out var prefix))
             {
                 codeAction.Title = $"{prefix}@using {@namespace}";
                 typeAccessibilityCodeActions.Add(codeAction.WrapResolvableCodeAction(context, LanguageServerConstants.CodeActions.Default));

src/Razor/src/Microsoft.AspNetCore.Razor.LanguageServer/CodeActions/Html/DefaultHtmlCodeActionProvider.cs

@@ -54,7 +54,7 @@ public static async Task RemapAndFixHtmlCodeActionEditAsync(IEditMappingService
 
             foreach (var edit in documentEdits)
             {
-                edit.Edits = HtmlFormatter.FixHtmlTestEdits(htmlSourceText, edit.Edits);
+                edit.Edits = HtmlFormatter.FixHtmlTextEdits(htmlSourceText, edit.Edits);
             }
 
             codeAction.Edit = new WorkspaceEdit