refactor: localStorageのaccountsはindexedDBで保持するように (#7609)

* accountsストアはindexedDBで保持するように

* fix lint

* fix indexeddb available detection

* remove debugging code

* fix lint

* resolve https://github.com/misskey-dev/misskey/pull/7609/files/ba756204b77ce6e1189b8443e9641f2d02119621#diff-f565878e8202f0037b830c780b7c0932dc1bb5fd3d05ede14d72d10efbc3740c
Firefoxでの動作を改善

* fix lint

* fix lint

* add changelog

src/client/scripts/idb-proxy.ts

@@ -0,0 +1,38 @@
+// FirefoxのプライベートモードなどではindexedDBが使用不可能なので、
+// indexedDBが使えない環境ではlocalStorageを使う
+import {
+	get as iget,
+	set as iset,
+	del as idel,
+	createStore,
+} from 'idb-keyval';
+
+const fallbackName = (key: string) => `idbfallback::${key}`;
+
+let idbAvailable = typeof window !== 'undefined' ? !!window.indexedDB : true;
+
+if (idbAvailable) {
+	try {
+		await createStore('keyval-store', 'keyval');
+	} catch (e) {
+		console.error('idb open error', e);
+		idbAvailable = false;
+	}
+}
+
+if (!idbAvailable) console.error('indexedDB is unavailable. It will use localStorage.');
+
+export async function get(key: string) {
+	if (idbAvailable) return iget(key);
+	return JSON.parse(localStorage.getItem(fallbackName(key)));
+}
+
+export async function set(key: string, val: any) {
+	if (idbAvailable) return iset(key, val);
+	return localStorage.setItem(fallbackName(key), JSON.stringify(val));
+}
+
+export async function del(key: string) {
+	if (idbAvailable) return idel(key);
+	return localStorage.removeItem(fallbackName(key));
+}