Remove ProjectSnapshotManagerDispatcher from RazorFileChangeDetector (#10278)

This change removes usage of `ProjectSnapshotManagerDispatcher` from
`RazorFileChangeDetector`. In order to achieve that, I've refactored
`RazorFileChangeDetector` to use an `AsyncBatchingWorkQueue` rather than
the existing complex strategy of tracking a dictionary of "pending
notifications" with delayed tasks. However, the `ProcessBatchAsync` is a
bit trickier than others I've implemented.

To reduce churn on the `RazorProjectService`, `RazorFileChangeDetector`
does extra work to try and avoid elide adds/remove pairs for the same
file. This makes the `ProcessBatchAsync` more complex because we need to
pass through the items in the batch once to find add/remove pairs and
make note of the changes we should skip. Then, we make a second pass and
notify the listeners of changes, taking care to step over skipped
changes we noted in the first pass. I hope the comments there clarify
the new strategy. The behavior should be approximately the same.

Author: DustinCampbell

src/Razor/src/Microsoft.AspNetCore.Razor.LanguageServer/IRazorFileChangeListener.cs

@@ -1,11 +1,13 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the MIT license. See License.txt in the project root for license information.
 
+using System.Threading;
+using System.Threading.Tasks;
 using Microsoft.AspNetCore.Razor.LanguageServer.Common;
 
 namespace Microsoft.AspNetCore.Razor.LanguageServer;
 
 internal interface IRazorFileChangeListener
 {
-    void RazorFileChanged(string filePath, RazorFileChangeKind kind);
+    Task RazorFileChangedAsync(string filePath, RazorFileChangeKind kind, CancellationToken cancellationToken);
 }

src/Razor/src/Microsoft.AspNetCore.Razor.LanguageServer/RazorFileChangeDetector.TestAccessor.cs

@@ -0,0 +1,44 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the MIT license. See License.txt in the project root for license information.
+
+using Microsoft.AspNetCore.Razor.LanguageServer.Common;
+using System.Threading.Tasks;
+using System;
+
+namespace Microsoft.AspNetCore.Razor.LanguageServer;
+
+internal partial class RazorFileChangeDetector
+{
+    internal TestAccessor GetTestAccessor() => new(this);
+
+    internal sealed class TestAccessor(RazorFileChangeDetector instance)
+    {
+        public void AddWork(string filePath, RazorFileChangeKind kind)
+        {
+            if (kind is not (RazorFileChangeKind.Added or RazorFileChangeKind.Removed))
+            {
+                throw new ArgumentException("Only adds and removes are allowed", nameof(kind));
+            }
+
+            instance._workQueue.AddWork((filePath, kind));
+        }
+
+        public void AddWork(params (string filePath, RazorFileChangeKind kind)[] items)
+        {
+            foreach (var (filePath, kind) in items)
+            {
+                if (kind is not (RazorFileChangeKind.Added or RazorFileChangeKind.Removed))
+                {
+                    throw new ArgumentException("Only adds and removes are allowed", nameof(items));
+                }
+            }
+
+            instance._workQueue.AddWork(items);
+        }
+
+        public Task WaitUntilCurrentBatchCompletesAsync()
+        {
+            return instance._workQueue.WaitUntilCurrentBatchCompletesAsync();
+        }
+    }
+}