Cache current process object to avoid performance hit (#5597)

* Read working set from Environment in ProcessInfo since it has better performance.

* Add unit test for ProcessInfo.

* Remove OSSkipCondition tag from process info unit test since it's cross-platform.

* Use Environment.WorkingSet in GetMemoryUsageInBytes.

src/Libraries/Microsoft.Extensions.Diagnostics.ResourceMonitoring/Windows/Interop/ProcessInfo.cs

@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System;
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 
@@ -41,7 +42,6 @@ public ulong GetMemoryUsage()
 
     public ulong GetCurrentProcessMemoryUsage()
     {
-        using Process process = Process.GetCurrentProcess();
-        return (ulong)process.WorkingSet64;
+        return (ulong)Environment.WorkingSet;
     }
 }

src/Libraries/Microsoft.Extensions.Diagnostics.ResourceMonitoring/Windows/WindowsSnapshotProvider.cs

@@ -109,8 +109,7 @@ internal static long GetCpuTicks()
 
     internal static long GetMemoryUsageInBytes()
     {
-        using var process = Process.GetCurrentProcess();
-        return process.WorkingSet64;
+        return Environment.WorkingSet;
     }
 
     internal static ulong GetTotalMemoryInBytes()

test/Libraries/Microsoft.Extensions.Diagnostics.ResourceMonitoring.Tests/Windows/ProcessInfoTests.cs

@@ -0,0 +1,23 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Microsoft.Extensions.Diagnostics.ResourceMonitoring.Windows.Interop;
+using Microsoft.TestUtilities;
+using Xunit;
+
+namespace Microsoft.Extensions.Diagnostics.ResourceMonitoring.Windows.Test;
+
+/// <summary>
+/// Process Info Interop Tests.
+/// </summary>
+/// <remarks>These tests are added for coverage reasons, but the code doesn't have
+/// the necessary environment predictability to really test it.</remarks>
+public sealed class ProcessInfoTests
+{
+    [ConditionalFact]
+    public void GetCurrentProcessMemoryUsage()
+    {
+        var workingSet64 = new ProcessInfo().GetCurrentProcessMemoryUsage();
+        Assert.True(workingSet64 > 0);
+    }
+}