Switch TextDocumentState.GetTextVersionAsync to ValueTask to reduce allocations. (#77213)

The task creation from calling this method accounts for 36 MB (0.2%) of allocations in the CSharpEditingTests.Completion speedometer test. Speedometer results with this change show marked improvement in these allocations.

Author: ToddGrun

src/Workspaces/Core/Portable/Workspace/Solution/ProjectState.cs

@@ -116,7 +116,7 @@ public ProjectState(LanguageServices languageServices, ProjectInfo projectInfo,
         DocumentStates = new TextDocumentStates<DocumentState>(projectInfoFixed.Documents, info => CreateDocument(info, parseOptions, loadTextOptions));
         AdditionalDocumentStates = new TextDocumentStates<AdditionalDocumentState>(projectInfoFixed.AdditionalDocuments, info => new AdditionalDocumentState(languageServices.SolutionServices, info, loadTextOptions));
 
-        _lazyLatestDocumentVersion = AsyncLazy.Create(static (self, c) => ComputeLatestDocumentVersionAsync(self.DocumentStates, self.AdditionalDocumentStates, c), arg: this);
+        _lazyLatestDocumentVersion = AsyncLazy.Create(static async (self, c) => await ComputeLatestDocumentVersionAsync(self.DocumentStates, self.AdditionalDocumentStates, c).ConfigureAwait(false), arg: this);
         _lazyLatestDocumentTopLevelChangeVersion = AsyncLazy.Create(static (self, c) => ComputeLatestDocumentTopLevelChangeVersionAsync(self.DocumentStates, self.AdditionalDocumentStates, c), arg: this);
 
         // ownership of information on document has moved to project state. clear out documentInfo the state is
@@ -220,7 +220,7 @@ private ProjectInfo FixProjectInfo(ProjectInfo projectInfo)
         return projectInfo;
     }
 
-    private static async Task<VersionStamp> ComputeLatestDocumentVersionAsync(TextDocumentStates<DocumentState> documentStates, TextDocumentStates<AdditionalDocumentState> additionalDocumentStates, CancellationToken cancellationToken)
+    private static async ValueTask<VersionStamp> ComputeLatestDocumentVersionAsync(TextDocumentStates<DocumentState> documentStates, TextDocumentStates<AdditionalDocumentState> additionalDocumentStates, CancellationToken cancellationToken)
     {
         // this may produce a version that is out of sync with the actual Document versions.
         var latestVersion = VersionStamp.Default;
@@ -1090,8 +1090,8 @@ private void GetLatestDependentVersions(
 
         if (recalculateDocumentVersion)
         {
-            dependentDocumentVersion = AsyncLazy.Create(static (arg, cancellationToken) =>
-                ComputeLatestDocumentVersionAsync(arg.newDocumentStates, arg.newAdditionalDocumentStates, cancellationToken),
+            dependentDocumentVersion = AsyncLazy.Create(static async (arg, cancellationToken) =>
+                await ComputeLatestDocumentVersionAsync(arg.newDocumentStates, arg.newAdditionalDocumentStates, cancellationToken).ConfigureAwait(false),
                 arg: (newDocumentStates, newAdditionalDocumentStates));
         }
         else if (contentChanged)

src/Workspaces/Core/Portable/Workspace/Solution/TextDocument.cs

@@ -90,8 +90,8 @@ internal SourceText GetTextSynchronously(CancellationToken cancellationToken)
     /// <summary>
     /// Gets the version of the document's text.
     /// </summary>
-    public Task<VersionStamp> GetTextVersionAsync(CancellationToken cancellationToken = default)
-        => State.GetTextVersionAsync(cancellationToken);
+    public async Task<VersionStamp> GetTextVersionAsync(CancellationToken cancellationToken = default)
+        => await State.GetTextVersionAsync(cancellationToken).ConfigureAwait(false);
 
     /// <summary>
     /// Fetches the current version for the document synchronously.

src/Workspaces/Core/Portable/Workspace/Solution/TextDocumentState.cs

@@ -123,7 +123,7 @@ public VersionStamp GetTextVersionSynchronously(CancellationToken cancellationTo
         return textAndVersion.Version;
     }
 
-    public async Task<VersionStamp> GetTextVersionAsync(CancellationToken cancellationToken)
+    public async ValueTask<VersionStamp> GetTextVersionAsync(CancellationToken cancellationToken)
     {
         // try fast path first
         if (TryGetTextVersion(out var version))