Clean up few more calls to object.freeze

- Fixed explicit casts hiding some type errors on object passed to `object.freeze` (too many properties or missing properties)
- Remove some extra casts
- Fixed casts of `Object.freeze` removing readonly

src/vs/workbench/api/common/extHostDocumentSaveParticipant.ts

@@ -106,7 +106,7 @@ export class ExtHostDocumentSaveParticipant implements ExtHostDocumentSavePartic
 		const { document, reason } = stubEvent;
 		const { version } = document;
 
-		const event = Object.freeze(<vscode.TextDocumentWillSaveEvent>{
+		const event = Object.freeze<vscode.TextDocumentWillSaveEvent>({
 			document,
 			reason,
 			waitUntil(p: Promise<any | vscode.TextEdit[]>) {