LayoutContainer support

[PhaserEditor2D]

Implement a LayoutContainer game object for laying out the children.

Some ideas until now:

• A LayoutContainer has a size.
• A LayoutContainer has a LayoutManager (BorderLayout, AnchorLayout, CardLayout, ColumnLayout, RowLayout, ...).
• Each child of a LayoutContainer may have a LayoutData related to the LayoutManager of the parent.
• The layout managers can be plugged into the editor.

[davyzhang]

if you intend to implement this, there might be a reference editor https://fairygui.com which I used extensively in other projects. It come with custom list/flexible layout/state management/timeline for animation etc.

Caveat: some of the implementations are expensive, might be better to separate them as plugins

[PhaserEditor2D]

Thanks @davyzhang. I will take a look. I think I someone mentioned this tool some time ago.