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/structures/ThreadView.tsx

@@ -329,8 +329,7 @@ export default class ThreadView extends React.Component<IProps, IState> {
                 <TimelinePanel
                     key={this.state.thread.id}
                     ref={this.timelinePanel}
-                    showReadReceipts={false} // Hide the read receipts
-                    // until homeservers speak threads language
+                    showReadReceipts={true}
                     manageReadReceipts={true}
                     manageReadMarkers={true}
                     sendReadReceiptOnLoad={true}