Add option to pause tweens during Substates switching.

• Haxe version: 4.3.1
• Flixel version: 5.4.0
• OpenFL version: 9.2.2
• Lime version: 8.0.2

So, usually, when I open a Substate in my state, any active tween keeps playing. But everything else stops updating (like it should). I suggest adding a variable to toggle that.
It worked for me with a slightly different code, but this should work aswell:

class FlxState extends FlxGroup
{
     public var keepTweensUpdate:Bool = true;

     // [...]

     function openSubState(SubState:FlxSubState)
     {
             @:privateAccess
             for (tween in FlxTween.globalManager._tweens)
		{
			tween.active = keepTweensUpdate;
		}

             // [...]
     }

     function closeSubState()
     {
             @:privateAccess
             for (tween in FlxTween.globalManager._tweens)
	     {
		tween.active = true;
	     }

     	     // [...]
     }

Start at FlxState.openSubState and closeSubState, then inspect how FlxTween.globalManager._tweens is updated during state switching. Determine where the proposed option belongs and verify that active tweens pause when requested and resume after the substate closes.