Read receipts for threads (#9239)

* Use EventType enum instead of hardcoded value

* Enable read receipts on thread timelines

* Strict null checks

* Strict null checks

* fix import group

* strict checks

* strict checks

* null check

* fix tests

src/components/views/rooms/EventTile.tsx

@@ -1333,6 +1333,7 @@ export class UnwrappedEventTile extends React.Component<IProps, IState> {
                         <a href={permalink} onClick={this.onPermalinkClicked}>
                             { timestamp }
                         </a>
+                        { msgOption }
                     </div>,
                     reactionsRow,
                 ]);