Rename FileChangeContext_FileChanged to be less ambiguous

There's going to be multiple contexts in here, so we should clarify
which one.

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

@@ -127,7 +127,7 @@ internal sealed class VisualStudioProject
                 _documentFileChangeContext = workspace.FileChangeWatcher.CreateContext();
             }
 
-            _documentFileChangeContext.FileChanged += FileChangeContext_FileChanged;
+            _documentFileChangeContext.FileChanged += DocumentFileChangeContext_FileChanged;
 
             // TODO: set this to watch the NuGet directory or the reference assemblies directory; since those change rarely and most references
             // will come from them, we can avoid creating a bunch of explicit file watchers.
@@ -651,7 +651,7 @@ public void RemoveAnalyzerReference(string fullPath)
 
         #endregion
 
-        private void FileChangeContext_FileChanged(object sender, string fullFilePath)
+        private void DocumentFileChangeContext_FileChanged(object sender, string fullFilePath)
         {
             _sourceFiles.ProcessFileChange(fullFilePath);
             _additionalFiles.ProcessFileChange(fullFilePath);