Fetch capabilities in the background (#4246)

* Fetch capabilities in the background

& keep them up to date

* Add missed await

* Replace some more runAllTimers

and round down the wait time for sanity

* Remove double comment

* Typo

* Add a method back that will fetch capabilities if they're not already there

* Add tests

* Catch exception here too

* Add test for room version code

src/matrix.ts

@@ -24,6 +24,7 @@ import { RoomWidgetClient, ICapabilities } from "./embedded";
 import { CryptoStore } from "./crypto/store/base";
 
 export * from "./client";
+export * from "./serverCapabilities";
 export * from "./embedded";
 export * from "./http-api";
 export * from "./autodiscovery";