Restrict LanguageServer IVTs to a specific namespace

[DustinCampbell]

Fixes #10096

Microsoft.VisualStudio.Razor.LanguageServerClient has a reference to Microsoft.AspNetCore.Razor.LanguageServer along with InternalsVisibleTo access. This is unavoidable because we currently run the LanguageServer in-proc in VS when the LSP editor is active. However, over time LanguageServerClient has relied on more and more code in LanguageServer, which can cause MS.ANC.Razor.LanguageServer to be loaded in VS when it shouldn't be. This change addresses this issue by limiting the types that LanguageServerClient has access to.

Access is restricted using the RestrictedInternalsVisibleToAttribute, which is already supported by Microsoft.CodeAnalysis.CSharp.BannedApiAnalyzers. Other than adding our own copy of this attribute and updating the AssemblyInfo.cs for MS.ANC.Razor.LanguageServer, this change is entirely mechanical. Essentially, I've just moved types around, and those types fall into two categories:

1. Types that are needed to host the language server. These have been moved to a Microsoft.AspNetCore.Razor.LanguageServer.Hosting namespace, and IVT is restricted to that namespace.
2. Protocol types that are needed by both the client and server. These have been moved to MS.CA.Razor.Workspaces and organized in a Protocol folder.

[DustinCampbell]

👀 The real change is in this file.

[DustinCampbell]

👀 Here's our definition of RestrictedInternalsVisibleToAttribute

[davidwengier]

I think there is probably more that could moved/abstracted out of Hosting and into workspaces (IClientConnection I think would be good, as it feels odd that so many endpoints have a using for the Hosting namespace), but this is still good as is.

[DustinCampbell]

I'm going to be out tomorrow. So, rather than "merge and run", I'll wait until Monday.