tree-view: first selected element should receive focus

[spike-rabbit]

Prerequisites

• I have read the Contributing Guidelines.
• I have not leaked any internal/restricted information like screenshots, videos, code snippets, links etc.

Affected component

si-tree-view

Summary

When a tree view receives focus, the first selected tree node should receive the focus.
See: https://www.w3.org/WAI/ARIA/apg/patterns/treeview/

Version

@siemens/element-ng: 49.x

Steps to reproduce

1. Go to tree-view example (playground for instance)
2. click on a note to activate it
3. tab out of the tree
4. tab in the tree

Code reproduction example

element-examples

What is the current bug behavior

First node has the focus.

What is the expected correct behavior

First selected node should have the focus.