FlxSpriteGroup cloning should keep positions of his children

• **Flixel 3.3.12 (probably last flixel too because the code behind clone() looks the same)
• OpenFL version: 3.6.1 (probably last openfl too)
• Lime version: 2.9.1 (probably last lime too)
• Affected targets: All I guess

Code snippet reproducing the issue:

package;

import flixel.FlxState;

class PlayState extends FlxState
{
    override public function create():Void
    {
        var group:FlxSpriteGroup = new FlxSpriteGroup();
        var p1:FlxSprite= new FlxSprite();
                p1.makeGraphic(200, 200, FlxColor.BLUE);
        p1.x = 50;
        p1.y = 50;
        var p2:FlxSprite= new FlxSprite();
                p2.makeGraphic(200, 200, FlxColor.RED);
        p2.x = 100;
        p2.y = 100;
        group.add(p1);
        group.add(p2);
        add(group);

               var group2 = group.clone();
        group2.setPosition(100, 0);
        add(group2);
    }
}

Observed behavior:
Clone the FlxSprites inside a FlxSpriteGroup but reset their positions to 0. (We don't see the 2 FlxSprites of group2). The clone() method of FlxSprite doesn't include copying the positions, that's probably not a problem for a single FlxSprite but for a group it's annoying.
Expected behavior:
Clone the FlxSprites inside a FlxSpriteGroup and keep their positions.

Start by tracing FlxSpriteGroup.clone and the FlxSprite.clone implementation described in the issue. Reproduce the example with two positioned sprites, then verify that the cloned group retains both child positions after group2.setPosition(100, 0).