Ensure we clean up RuleSetFiles when we close the solution

The VisualStudioRuleSetManager is a singleton that acts as a cache
of RuleSetFiles and also manages the lifetime of file watching. We
never cleaned that up when we shut down VS, so we leaked a bunch of
file watchers, which would throw during finalization asserting they
weren't cleaned up and bring down the process with it.

src/VisualStudio/Core/Def/Implementation/ProjectSystem/RuleSets/VisualStudioRuleSetManager.cs

@@ -41,7 +41,7 @@ private void StopTrackingRuleSetFile(RuleSetFile ruleSetFile)
             _ruleSetFileMap.Remove(ruleSetFile.FilePath);
         }
 
-        public void Dispose()
+        public void ClearCachedRuleSetFiles()
         {
             foreach (var pair in _ruleSetFileMap)
             {
@@ -50,5 +50,10 @@ public void Dispose()
 
             _ruleSetFileMap.Clear();
         }
+
+        void IDisposable.Dispose()
+        {
+            ClearCachedRuleSetFiles();
+        }
     }
 }

src/VisualStudio/Core/Def/Implementation/ProjectSystem/VisualStudioProjectTracker.cs

@@ -24,7 +24,7 @@
 
 namespace Microsoft.VisualStudio.LanguageServices.Implementation.ProjectSystem
 {
-    internal sealed partial class VisualStudioProjectTracker : ForegroundThreadAffinitizedObject, IDisposable, IVisualStudioHostProjectContainer
+    internal sealed partial class VisualStudioProjectTracker : ForegroundThreadAffinitizedObject, IVisualStudioHostProjectContainer
     {
         #region Readonly fields
         private static readonly ConditionalWeakTable<SolutionId, string> s_workingFolderPathMap = new ConditionalWeakTable<SolutionId, string>();
@@ -244,14 +244,6 @@ public void InitializeProviders(DocumentProvider documentProvider, VisualStudioM
         public VisualStudioMetadataReferenceManager MetadataReferenceProvider { get; private set; }
         public VisualStudioRuleSetManager RuleSetFileProvider { get; private set; }
 
-        public void Dispose()
-        {
-            if (this.RuleSetFileProvider != null)
-            {
-                this.RuleSetFileProvider.Dispose();
-            }
-        }
-
         internal AbstractProject GetProject(ProjectId id)
         {
             lock (_gate)
@@ -565,6 +557,8 @@ public void OnAfterCloseSolution()
                 _projectPathToIdMap.Clear();
             }
 
+            RuleSetFileProvider.ClearCachedRuleSetFiles();
+
             foreach (var workspaceHost in _workspaceHosts)
             {
                 workspaceHost.SolutionClosed();

src/VisualStudio/TestUtilities2/ProjectSystemShim/Framework/TestEnvironment.vb

@@ -87,8 +87,8 @@ Namespace Microsoft.VisualStudio.LanguageServices.UnitTests.ProjectSystemShim.Fr
                 project.Disconnect()
             Next
 
+            _projectTracker.OnAfterCloseSolution()
             _workspace.Dispose()
-            _projectTracker.Dispose()
 
             For Each filePath In _projectFilePaths
                 File.Delete(filePath)