fixed flawed API deprecation warning

We want to warn when extensions change `CompletionItem#insertText` during resolve but the check be better correct...

Author: jrieken

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

@@ -1040,14 +1040,22 @@ class CompletionsAdapter {
 			additionalTextEdits: resolvedItem.additionalTextEdits
 		};
 
-		if (item.insertText !== resolvedItem.insertText) {
+		if (CompletionsAdapter._insertTextIdent(item.insertText) !== CompletionsAdapter._insertTextIdent(resolvedItem.insertText)) {
 			this._apiDeprecation.report('CompletionItem.insertText', this._extension, 'extension MAY NOT change \'insertText\' of a CompletionItem during resolve');
 			enforcedResolvedItem.insertText = resolvedItem.insertText;
 		}
 
 		return this._convertCompletionItem(enforcedResolvedItem, id);
 	}
 
+	private static _insertTextIdent(insertText: string | vscode.SnippetString | undefined) {
+		switch (typeof insertText) {
+			case 'string': return insertText;
+			case 'undefined': return undefined;
+			case 'object': return insertText.value;
+		}
+	}
+
 	releaseCompletionItems(id: number): any {
 		this._disposables.get(id)?.dispose();
 		this._disposables.delete(id);