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/rooms/PresenceLabel.tsx

@@ -82,7 +82,7 @@ export default class PresenceLabel extends React.Component<IProps> {
         }
     }
 
-    public render() {
+    public render(): JSX.Element {
         return (
             <div className="mx_PresenceLabel">
                 {this.getPrettyPresence(this.props.presenceState, this.props.activeAgo, this.props.currentlyActive)}