Disable presenting scores in online song selects

[bdach]

RFC. Closes #36815 I guess.

Song select V1 completely disabled the ability to view a score outside of solo play in ways that are very easy to let fly under the radar:

osu/osu.Game/Screens/Select/Leaderboards/BeatmapLeaderboard.cs

Line 26 in 5fc836d

public Action<ScoreInfo>? ScoreSelected;

osu/osu.Game/Screens/Select/PlaySongSelect.cs

Lines 47 to 53 in 46db3ad

	playBeatmapDetailArea = new PlayBeatmapDetailArea
	{
	Leaderboard =
	{
	ScoreSelected = PresentScore
	}
	};

therefore the issue this is trying to close would never even manifest there.

The direct cause of the issue is that the results screen is pushed to the relevant online screen's substack of screens rather than the game-global parent stack. That means that when the back button is pressed, the following logic fires:

osu/osu.Game/Screens/OnlinePlay/OnlinePlayScreen.cs

Lines 174 to 189 in 6fa4a71

	public override bool OnBackButton()
	{
	if (!(screenStack.CurrentScreen is IOnlinePlaySubScreen onlineSubScreen))
	return false;
	if (((Drawable)onlineSubScreen).IsLoaded && onlineSubScreen.AllowUserExit && onlineSubScreen.OnBackButton())
	return true;
	if (screenStack.CurrentScreen != null && !(screenStack.CurrentScreen is LoungeSubScreen))
	{
	screenStack.Exit();
	return true;
	}
	return false;
	}

This logic fires on the parent screen even though the child screen is the one the user is attempting to back out of. And none of the exemptions for the screen substack inside of the above method fire because the subscreen is not an IOnlinePlaySubScreen (it's SoloResultsScreen in this case).

Now the direct cause here is probably fixable, although possibly not without some significant pulling of footer-shaped teeth. However, I kind of question as to why viewing scores should be permitted on online song selects in the first place - it kind of distracts from the primary purpose of the screens which is to just pick a map already.