Support "Type ahead" in TreeView (See the APG's Keyboard interaction in a TreeView)

[emyarod]

ref #6792

APG Keyboard interaction in treeview

• Type-ahead is recommended for all trees, especially for trees with more than 7 root nodes:
  • Type a character: focus moves to the next node with a name that starts with the typed character.
  • Type multiple characters in rapid succession: focus moves to the next node with a name that starts with the string of characters typed.