refactor: clear client caches on stop request (#1374)

The command to restart the language server calls `client.stop` followed
by `client.start`. We should clear the caches so that the restart
command starts with a clean state.

Author: atscott

client/src/client.ts

@@ -236,6 +236,8 @@ export class AngularLanguageClient implements vscode.Disposable {
     this.outputChannel.clear();
     this.dispose();
     this.client = null;
+    this.fileToIsInAngularProjectMap.clear();
+    this.virtualDocumentContents.clear();
   }
 
   /**