Focus the thread panel when clicking on an item in the TAC (#12410)

* Focus the thread panel when clicking on an item in the TAC

actually the 'close' button in the threads panel as it's the only
interactive element: we can improve this later when we use landmarks
& generally have better a11y.

* Undo minor refactoring

as none of it is test3ed, it's not worth it.

* add unit test

* Add matrixchat tests

* Needs awaits

* ts-ignore

* Fix test (I think...)

* Remove unnecessary value set

* Not how assignments work

src/components/structures/RoomView.tsx

@@ -1268,7 +1268,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
             case Action.FocusAComposer: {
                 dis.dispatch<FocusComposerPayload>({
                     ...(payload as FocusComposerPayload),
-                    // re-dispatch to the correct composer
+                    // re-dispatch to the correct composer (the send message will still be on screen even when editing a message)
                     action: this.state.editState ? Action.FocusEditMessageComposer : Action.FocusSendMessageComposer,
                 });
                 break;