Fix closing all modals (#12728)

* Fix closing all modals

We used `Modal.closeCurrentModal()` in a bunch of places, in all cases
(as far as I can see: it wasn't commented) we meant to close all open
modals. This swaps that function for one that closes all open modals.

Also types the close reason which claimed to be something in a comment,
of course, was wrong because a load of places passed their own random
string which was never used.

* Force close modals

* Try with minimal changes

* Already had a method for this

* Add test

* More tests

* Unused importsd

src/components/structures/MatrixChat.tsx

@@ -1544,7 +1544,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
             if (Lifecycle.isLoggingOut()) return;
 
             // A modal might have been open when we were logged out by the server
-            Modal.closeCurrentModal("Session.logged_out");
+            Modal.forceCloseAllModals();
 
             if (errObj.httpStatus === 401 && errObj.data && errObj.data["soft_logout"]) {
                 logger.warn("Soft logout issued by server - avoiding data deletion");