refactor(frontend): use* 関数の格納場所のフォルダ名を composables に変更 (#16004)

* refactor(frontend): use* 関数の格納場所を正式名称（composables）に変更

* migrate

* move useLoading

packages/frontend/src/composables/use-mutation-observer.ts

@@ -0,0 +1,21 @@
+/*
+ * SPDX-FileCopyrightText: syuilo and misskey-project
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { onUnmounted, watch } from 'vue';
+import type { Ref } from 'vue';
+
+export function useMutationObserver(targetNodeRef: Ref<HTMLElement | null | undefined>, options: MutationObserverInit, callback: MutationCallback): void {
+	const observer = new MutationObserver(callback);
+
+	watch(targetNodeRef, (targetNode) => {
+		if (targetNode) {
+			observer.observe(targetNode, options);
+		}
+	}, { immediate: true });
+
+	onUnmounted(() => {
+		observer.disconnect();
+	});
+}