RoomListViewModel: Support primary filters in the view model (#29454)

* Track available filters and expose this info from the vm

- Adds a separate hook that tracks the filtered rooms and the available
  filters.
- When secondary filters are added, some of the primary filters will be
  selectively hidden. So track this info in the vm.

* Write tests

* Fix typescript error

* Fix translation

* Explain what a primary filter is

test/unit-tests/components/views/rooms/RoomListPanel/RoomList-test.tsx

@@ -27,7 +27,7 @@ describe("<RoomList />", () => {
 
         matrixClient = stubClient();
         const rooms = Array.from({ length: 10 }, (_, i) => mkRoom(matrixClient, `room${i}`));
-        vm = { rooms, openRoom: jest.fn() };
+        vm = { rooms, openRoom: jest.fn(), primaryFilters: [] };
 
         // Needed to render a room list cell
         DMRoomMap.makeShared(matrixClient);