Enable VSTHRD109 (Switch instead of assert in async methods) and fix violations

Author: sharwell

GitCommands/RevisionReader.cs

@@ -63,7 +63,7 @@ private async Task ExecuteAsync(
             string pathFilter,
             [CanBeNull] Func<GitRevision, bool> revisionPredicate)
         {
-            ThreadHelper.ThrowIfNotOnUIThread();
+            await ThreadHelper.JoinableTaskFactory.SwitchToMainThreadAsync();
 
             var token = _cancellationTokenSequence.Next();
 

GitExtensions.ruleset

@@ -7,7 +7,6 @@
   </Rules>
   <Rules AnalyzerId="Microsoft.VisualStudio.Threading.Analyzers" RuleNamespace="Microsoft.VisualStudio.Threading.Analyzers">
     <Rule Id="VSTHRD010" Action="None" />
-    <Rule Id="VSTHRD109" Action="None" />
     <Rule Id="VSTHRD110" Action="None" />
   </Rules>
   <Rules AnalyzerId="StyleCop.Analyzers" RuleNamespace="StyleCop.Analyzers">

GitUI/BranchTreePanel/RepoObjectsTree.cs

@@ -57,7 +57,7 @@ public void SetBranchFilterer(FilterBranchHelper filterBranchHelper)
 
         public async Task ReloadAsync()
         {
-            ThreadHelper.ThrowIfNotOnUIThread();
+            await this.SwitchToMainThreadAsync();
 
             var token = CancelBackgroundTasks();
             Enabled = false;