Kiwi tree

[MartynasStrazdas]

Early preview of how the kiwi tree looks.

There are plenty of things that are not yet released from kiwi side, that we want:

1. Separate error nodes: will be provided eventually
2. Action items wrapper: so far can't provide use case or check if we need it as actions don't seem to work as intended with icons.
3. Multiline label: for now only label is available, sublabel should be added by kiwi.
4. Size for tree items: size is removed, component has property density to control size of all components.
5. ...

Tree renderer property name changes so far:
IsSelected => selected
isDisabled => aria-disabled (need to figure out if we want a separate prop)

General:

1. Icons are now provided through Href, but it seems all tree will continue to support basic svg (actions/node icons).
2. There is no to little changes for using new TreeRenderer.

Tree preview:

tree-preview.mp4

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[saskliutas]

Looks good for an initial attempt. Should be enough to integrate into tree-widget.