add validator functions for backend-api types

src/Umbraco.Web.UI.Client/src/shared/resources/apiTypeValidators.function.ts

@@ -0,0 +1,13 @@
+import type { ApiError, CancelError, CancelablePromise } from '@umbraco-cms/backoffice/backend-api';
+
+export function isApiError(error: unknown): error is ApiError {
+	return (error as ApiError).name === 'ApiError';
+}
+
+export function isCancelError(error: unknown): error is CancelError {
+	return (error as CancelError).name === 'CancelError';
+}
+
+export function isCancelablePromise<T>(promise: unknown): promise is CancelablePromise<T> {
+	return (promise as CancelablePromise<T>).cancel !== undefined;
+}