Autosize node based on children

[wouterlucas]

Add autosize to a node to dynamically update its size based on children's matrix3d.

• Reuse of autosize property
• If node has a texture, that behavior will be prioritized (to not break existing behavior)
• If node does not have a texture, w/h are automatically adjusted to envelop children

notes:

• Does not grow "backward" so only beyond its own x,y anchor left + down
• Although optimized, this is not "for free" as it will involve additional calculations

PR includes unit tests and VRT testcase.

Useful for Touch/Point usecases where you want the parent to be clickable and may provide utility for flexbox usage.