src/vs/workbench/common/editor.ts/isSideBySideEditorInput
function isSideBySideEditorInput(obj: unknown): obj is ISideBySideEditorInput {
	const sideBySideEditorInput = obj as ISideBySideEditorInput | undefined;
	if (!sideBySideEditorInput) {
		return false;
	}

	return !!sideBySideEditorInput.primary && !!sideBySideEditorInput.secondary;
}