Layout group children auto-spacing

[LeXXik]

Forum topic: https://forum.playcanvas.com/t/layout-question/14045

https://developer.playcanvas.com/en/api/pc.LayoutGroupComponent.html
Feature request: add an option for pc.LayoutGroupComponent to auto space its children.

[jpauloruschel]

I really like this idea. Thinking about how to expose this functionality: how about a separate option in the fitting options? Currently we have None, Stretch, Shrink and Both, the last 3 of which alter the positions and sizes of the children. We would then add another option like Space, which only alters the positions, but not the sizes. I think there's no use-case to have resizes + auto spacing.