hierarchies-react: Update tree and tree node renderers to use iTwinUI v5

[grigasp]

Now that the first 5.0-alpha of iTwinUI is out, we should start the work of updating our renderers to use the new APIs. The goals:

• Identify missing pieces and bugs as early as possible and let iTwinUI team know about that.
• Do as much work as possible before the full iTwinUI 5.0 release so we can do our own release quickly afterwards.

This is likely take multiple PRs and span a long period of time. And we don't want to release until we consume the full 5.0. So I suggest setting up a protected branch and doing all the work there.

Tasks

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1. Tree state: loading root nodes
2. Tree state: failed to load root nodes
3. Parent node state: loading children
4. Parent node state: failed to load children
5. Parent node state: children limit exceeded
6. Node state: selected
7. Node state: hovered
8. Child nodes state: parent selected
9. Action buttons support

[grigasp]

Added a list of tasks - see issue description