Enable lint rules for Promise handling to discourage misuse of them. (#2607)

* Enable lint rules for Promise handling to discourage misuse of them.
Squashed all of Hugh's commits into one.

---------

Co-authored-by: Hugh Nimmo-Smith <hughns@element.io>

src/state/CallViewModel.ts

@@ -279,7 +279,7 @@ export class CallViewModel extends ViewModel {
                   });
               }),
               // Then unhold them
-            ]).then(() => Promise.resolve({ unhold: ps })),
+            ]).then(() => ({ unhold: ps })),
           );
         } else {
           return EMPTY;