[Tree] Parents of selected nodes

[tleunen]

I've been thinking about a few things in the Tree component and playing with both The Aria Tree, as well as the Spectrum Treeview. Both behave exactly the same, which is alright.

Currently, selecting a node doesn't affect any of the parents visually. And I think this behavior could make sense in some places. Although, I also think that it makes sense for the parent to receive an "indeterminate" state when some of their children are selected, and probably be fully selected when all children are selected. (Maybe under a new selection behavior?)

In that same philosophy, there's also a need to automatically select all the children when you select a parent. (Although that part can easily be done by the consumer)

Am I seeing a selectable tree the wrong way, or would this make sense?