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/widgets/Jitsi.ts

@@ -61,7 +61,7 @@ export class Jitsi {
         return null;
     }
 
-    public start() {
+    public start(): void {
         const cli = MatrixClientPeg.get();
         cli.on(ClientEvent.ClientWellKnown, this.update);
         // call update initially in case we missed the first WellKnown.client event and for if no well-known present

src/widgets/ManagedHybrid.ts

@@ -45,7 +45,7 @@ export function isManagedHybridWidgetEnabled(): boolean {
     return !!getWidgetBuildUrl();
 }
 
-export async function addManagedHybridWidget(roomId: string) {
+export async function addManagedHybridWidget(roomId: string): Promise<void> {
     const cli = MatrixClientPeg.get();
     const room = cli.getRoom(roomId);
     if (!room) {