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/components/views/audio_messages/Clock.tsx

@@ -43,7 +43,7 @@ export default class Clock extends React.Component<Props> {
         return currentFloor !== nextFloor;
     }
 
-    public render() {
+    public render(): JSX.Element {
         return (
             <span aria-live={this.props["aria-live"]} role={this.props.role} className="mx_Clock">
                 {this.props.formatFn(this.props.seconds)}