Make invited room behavior prettier and sleeker

[kevinaboos]

Although the room InviteScreen is fully functional and works properly, there are still some ways we could make it a bit nicer looking and sleeker.

• Upon showing the InviteScreen (in set_displayed_invite()), change the join button icon to an "enter room" icon, and set the button as enabled and the button text to be "Join room".
• Once the join button has been clicked, change the icon to a loading spinner and the text to "Joining...".
  • This will require a special button type that can show other non-icon content. Alternatively, we could hide the button temporarily and just show a LoadingSpinner with a background frame that looks like a disabled button... that might be easier.
• Once the JoinRoomResultAction::Joined has been received, change the button icon to a green checkmark: " ✅ Joined!"
• Close rooms when they are successfully Left.
  • We can now do this because navigation between rooms has recently been implemented. See how we achieve this to close a tombstoned room when its successor has been joined:

    robrix/src/app.rs

    Lines 536 to 593 in d7117c3

    	fn navigate_to_room(
    	&mut self,
    	cx: &mut Cx,
    	room_to_close: Option<&OwnedRoomId>,
    	destination_room: &BasicRoomDetails,
    	) {
    	// A closure that closes the given `room_to_close`, if it exists in an open tab.
    	let close_room_closure_opt = room_to_close.map(|to_close| {
    	let tab_id = LiveId::from_str(to_close.as_str());
    	let widget_uid = self.ui.widget_uid();
    	move |cx: &mut Cx| {
    	cx.widget_action(
    	widget_uid,
    	&HeapLiveIdPath::default(),
    	DockAction::TabCloseWasPressed(tab_id),
    	);
    	enqueue_rooms_list_update(RoomsListUpdate::HideRoom { room_id: to_close.clone() });
    	}
    	});
    	// If the successor room is not loaded, show a join modal.
    	let destination_room_id = destination_room.room_name_id.room_id();
    	if !cx.get_global::<RoomsListRef>().is_room_loaded(destination_room_id) {
    	log!("Destination room {} not loaded, showing join modal...", destination_room_id);
    	self.waiting_to_navigate_to_joined_room = Some((
    	destination_room.clone(),
    	room_to_close.cloned(),
    	));
    	cx.action(JoinLeaveRoomModalAction::Open {
    	kind: JoinLeaveModalKind::JoinRoom(destination_room.clone()),
    	show_tip: false,
    	});
    	return;
    	}
    	log!(
    	"Navigating to destination room {} ({}), closing room {room_to_close:?}",
    	destination_room_id,
    	destination_room.room_name_id
    	);
    	// Select and scroll to the destination room in the rooms list.
    	let new_selected_room = SelectedRoom::JoinedRoom {
    	room_name_id: destination_room.room_name_id.clone(),
    	};
    	enqueue_rooms_list_update(RoomsListUpdate::ScrollToRoom(destination_room_id.clone()));
    	cx.widget_action(
    	self.ui.widget_uid(),
    	&HeapLiveIdPath::default(),
    	RoomsListAction::Selected(new_selected_room),
    	);
    	// Close a previously/currently-open room if specified.
    	if let Some(closure) = close_room_closure_opt {
    	closure(cx);
    	}
    	}
    	}