[Debugger] Fix tooltips in razor and other projection buffers

Fixes https://devdiv.visualstudio.com/DevDiv/_workitems/edit/1020677

Author: sandyarmstrong

main/src/addins/MonoDevelop.Debugger/MonoDevelop.Debugger.VSTextView/QuickInfo/DebuggerQuickInfoSource.cs

@@ -152,7 +152,7 @@ private async Task EvaluateAndShowTooltipAsync (IAsyncQuickInfoSession session,
 
 #if MAC
 			var location = new PinnedWatchLocation (textDocument?.FilePath);
-			var snapshot = view.TextDataModel.DocumentBuffer.CurrentSnapshot;
+			var snapshot = textBuffer.CurrentSnapshot;
 			int line, column;
 
 			var start = debugInfo.Span.GetStartPoint (snapshot);