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>

---------

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

src/utils/membership.ts

@@ -131,3 +131,23 @@ export async function waitForMember(
         client.removeListener(RoomStateEvent.NewMember, handler);
     });
 }
+
+/**
+ * Check if the user is the only joined admin in the room
+ * This function will *not* cause lazy loading of room members, so if these should be included then
+ * the caller needs to make sure members have been loaded.
+ * @param room The room to check if the user is the only admin.
+ * @returns True if the user is the only user with the highest power level, false otherwise
+ */
+export function isOnlyAdmin(room: Room): boolean {
+    const currentUserLevel = room.getMember(room.client.getSafeUserId())?.powerLevel;
+
+    const userLevelValues = room.getJoinedMembers().map((m) => m.powerLevel);
+
+    const maxUserLevel = Math.max(...userLevelValues.filter((x) => typeof x === "number"));
+    // If the user is the only user with highest power level
+    return (
+        maxUserLevel === currentUserLevel &&
+        userLevelValues.lastIndexOf(maxUserLevel) == userLevelValues.indexOf(maxUserLevel)
+    );
+}