Enable @typescript-eslint/explicit-function-return-type in /src (#9788)

* Enable `@typescript-eslint/explicit-member-accessibility` on /src

* Prettier

* Enable `@typescript-eslint/explicit-function-return-type` in /src

* Fix types

* tsc strict fixes

* Delint

* Fix test

* Fix bad merge

src/stores/AsyncStoreWithClient.ts

@@ -52,17 +52,17 @@ export abstract class AsyncStoreWithClient<T extends Object> extends AsyncStore<
         return this.readyStore.mxClient;
     }
 
-    protected async onReady() {
+    protected async onReady(): Promise<void> {
         // Default implementation is to do nothing.
     }
 
-    protected async onNotReady() {
+    protected async onNotReady(): Promise<void> {
         // Default implementation is to do nothing.
     }
 
     protected abstract onAction(payload: ActionPayload): Promise<void>;
 
-    protected async onDispatch(payload: ActionPayload) {
+    protected async onDispatch(payload: ActionPayload): Promise<void> {
         await this.onAction(payload);
     }
 }