Test typescriptification - MessagePanel (#8943)

* mv test/components/structures/MessagePanel-test.js test/components/structures/MessagePanel-test.tsx

* convert simpler messagepanel tests to rtl

* add data-testid to eventlistsummary

* convert read marker tests to rtl

* formatting

* remove commented

src/components/structures/MessagePanel.tsx

@@ -1313,6 +1313,7 @@ class MainGrouper extends BaseGrouper {
         ret.push(
             <EventListSummary
                 key={key}
+                data-testid={key}
                 events={this.events}
                 onToggle={panel.onHeightChanged} // Update scroll state
                 startExpanded={highlightInSummary}