Add type annotation for some js files (#24787)

app/javascript/types/resources.ts

@@ -1,8 +1,4 @@
-interface MastodonMap<T> {
-  get<K extends keyof T>(key: K): T[K];
-  has<K extends keyof T>(key: K): boolean;
-  set<K extends keyof T>(key: K, value: T[K]): this;
-}
+import type { MastodonMap } from './util';
 
 type AccountValues = {
   id: number;

app/javascript/types/util.ts

@@ -0,0 +1,7 @@
+export interface MastodonMap<T> {
+  get<K extends keyof T>(key: K): T[K];
+  has<K extends keyof T>(key: K): boolean;
+  set<K extends keyof T>(key: K, value: T[K]): this;
+}
+
+export type ValueOf<T> = T[keyof T];