Refactor useIsRoomE2EE

Make it take a room object rather than a room ID to avoid it depending
on a side effect, ie. if the room object input changes, the hook will be
re-run but if we can't get the room from the room ID for whatever reason,
we'd be stuck.

Also add logging on why we decided a room was e2ee.

src/room/RoomPage.tsx

@@ -110,7 +110,7 @@ export const RoomPage: FC = () => {
       {content}
       {/* On Android and iOS, show a prompt to launch the mobile app. */}
       {appPrompt && (platform === "android" || platform === "ios") && (
-        <AppSelectionModal roomId={roomId} />
+        <AppSelectionModal roomId={roomId ?? undefined} />
       )}
     </>
   );