[Bugfix]: react-tree fix navigation on selection tree

[bsunderhus]

The Tree components should provide navigation according to WAI-ARIA documentation:

When a single-select tree receives focus:

• If none of the nodes are selected before the tree receives focus, focus is set on the first node.
• If a node is selected before the tree receives focus, focus is set on the selected node.

When a multi-select tree receives focus:

• If none of the nodes are selected before the tree receives focus, focus is set on the first node.
• If one or more nodes are selected before the tree receives focus, focus is set on the first selected node.

[bsunderhus]

@petdud What happens if the tree nodes are all closed? do we open then to focus on the selected node?

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