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/extHostConfiguration.ts

@@ -277,7 +277,7 @@ export class ExtHostConfigProvider {
 			mixin(result, config, false);
 		}
 
-		return <vscode.WorkspaceConfiguration>Object.freeze(result);
+		return Object.freeze(result);
 	}
 
 	private _toReadonlyValue(result: any): any {

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

@@ -191,7 +191,7 @@ export class DiagnosticCollection implements vscode.DiagnosticCollection {
 		this._checkDisposed();
 		const result = this.#data.get(uri);
 		if (Array.isArray(result)) {
-			return <ReadonlyArray<vscode.Diagnostic>>Object.freeze(result.slice(0));
+			return Object.freeze(result.slice(0));
 		}
 		return [];
 	}

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[]>) {