Update for compatibility with v12 rooms (#30452)

* Update for compatibility with v12 rooms

Stop using powerLevelNorm and reading PL events manually.

To support https://github.com/matrix-org/matrix-js-sdk/pull/4937

* Add test for leave space dialog

* Don't compute stuff if we don't need it

* Use room.client

* Use getSafeUserId

* Remove client arg

* Use getJoinedMembers

and add doc

* Fix tests

* Fix more tests

* Fix other test

* Clarify comment

Co-authored-by: Michael Telatynski <7t3chguy@gmail.com>

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Co-authored-by: Michael Telatynski <7t3chguy@gmail.com>

src/components/views/dialogs/LeaveSpaceDialog.tsx

@@ -15,23 +15,13 @@ import BaseDialog from "../dialogs/BaseDialog";
 import SpaceStore from "../../../stores/spaces/SpaceStore";
 import SpaceChildrenPicker from "../spaces/SpaceChildrenPicker";
 import { filterBoolean } from "../../../utils/arrays";
+import { isOnlyAdmin } from "../../../utils/membership";
 
 interface IProps {
     space: Room;
     onFinished(leave: boolean, rooms?: Room[]): void;
 }
 
-const isOnlyAdmin = (room: Room): boolean => {
-    const userId = room.client.getSafeUserId();
-    if (room.getMember(userId)?.powerLevelNorm !== 100) {
-        return false; // user is not an admin
-    }
-    return room.getJoinedMembers().every((member) => {
-        // return true if every other member has a lower power level (we are highest)
-        return member.userId === userId || member.powerLevelNorm < 100;
-    });
-};
-
 const LeaveSpaceDialog: React.FC<IProps> = ({ space, onFinished }) => {
     const spaceChildren = useMemo(() => {
         const roomSet = new Set(SpaceStore.instance.getSpaceFilteredRoomIds(space.roomId));