src/vs/workbench/services/userDataSync/browser/userDataSyncWorkbenchService.ts/isMergeEditorInput
export function isMergeEditorInput(editor: unknown): editor is MergeEditorInput {
	const candidate = editor as MergeEditorInput;
	return URI.isUri(candidate?.base) && URI.isUri(candidate?.input1?.uri) && URI.isUri(candidate?.input2?.uri) && URI.isUri(candidate?.result);
}