Avoid checking the CanonicalName each time for the analyzer

If the user expands a node in a CPS project wanting to look at the
diagnostics under an analyzer, but we haven't been told about that
analyzer let, we stick a WorkspaceChanged handler there to find it once
it comes back. We were hopping to the UI thread to see if the
CanonicalName of the item could have changed, but that's not really
going to happen ever for these items, so we can just grab it once
during creation and be done with it.

Author: jasonmalinowski

src/VisualStudio/Core/Impl/SolutionExplorer/DiagnosticItem/CpsDiagnosticItemSource.cs

@@ -19,6 +19,7 @@ internal sealed partial class CpsDiagnosticItemSource : BaseDiagnosticAndGenerat
 {
     private readonly IVsHierarchyItem _item;
     private readonly string _projectDirectoryPath;
+    private readonly string? _analyzerFilePath;
 
     private WorkspaceEventRegistration? _workspaceChangedDisposer;
 
@@ -37,6 +38,8 @@ public CpsDiagnosticItemSource(
         _item = item;
         _projectDirectoryPath = Path.GetDirectoryName(projectPath);
 
+        _analyzerFilePath = CpsUtilities.ExtractAnalyzerFilePath(_projectDirectoryPath, _item.CanonicalName);
+
         this.AnalyzerReference = TryGetAnalyzerReference(Workspace.CurrentSolution);
         if (this.AnalyzerReference == null)
         {
@@ -47,9 +50,7 @@ public CpsDiagnosticItemSource(
             // then connect to it.
             if (workspace.CurrentSolution.ContainsProject(projectId))
             {
-                // Main thread dependency as OnWorkspaceChangedLookForAnalyzer accesses the IVsHierarchy
-                // and fires the PropertyChanged event 
-                _workspaceChangedDisposer = Workspace.RegisterWorkspaceChangedHandler(OnWorkspaceChangedLookForAnalyzer, WorkspaceEventOptions.RequiresMainThreadOptions);
+                _workspaceChangedDisposer = Workspace.RegisterWorkspaceChangedHandler(OnWorkspaceChangedLookForAnalyzer);
                 item.PropertyChanged += IVsHierarchyItem_PropertyChanged;
 
                 // Now that we've subscribed, check once more in case we missed the event
@@ -118,14 +119,11 @@ private void OnWorkspaceChangedLookForAnalyzer(WorkspaceChangeEventArgs e)
             return null;
         }
 
-        var canonicalName = _item.CanonicalName;
-        var analyzerFilePath = CpsUtilities.ExtractAnalyzerFilePath(_projectDirectoryPath, canonicalName);
-
-        if (string.IsNullOrEmpty(analyzerFilePath))
+        if (string.IsNullOrEmpty(_analyzerFilePath))
         {
             return null;
         }
 
-        return project.AnalyzerReferences.FirstOrDefault(r => string.Equals(r.FullPath, analyzerFilePath, StringComparison.OrdinalIgnoreCase));
+        return project.AnalyzerReferences.FirstOrDefault(r => string.Equals(r.FullPath, _analyzerFilePath, StringComparison.OrdinalIgnoreCase));
     }
 }