Support custom tags in the room list again

Fixes https://github.com/vector-im/riot-web/issues/14091

Design needs work, however this is behind labs anyways. This re-implements the behaviour of the old room list.

The implementation ended up being a lot easier due to early confusion with what the TagOrderStore and TagPanel take care of. Turns out they don't deal with tags, but groups. As such, we don't need to do anything with filtering (though we keep some sanity checks in place for safety), and just have to wire up the CustomRoomTagPanel and CustomRoomTagStore.

src/utils/enums.ts

@@ -25,3 +25,13 @@ export function getEnumValues<T>(e: any): T[] {
         .filter(k => ['string', 'number'].includes(typeof(e[k])))
         .map(k => e[k]);
 }
+
+/**
+ * Determines if a given value is a valid value for the provided enum.
+ * @param e The enum to check against.
+ * @param val The value to search for.
+ * @returns True if the enum contains the value.
+ */
+export function isEnumValue<T>(e: T, val: string | number): boolean {
+    return getEnumValues(e).includes(val);
+}