NOTE: This was manually landed with some changes in fb4f0d08.
This will allow the user to navigate through a hierarchy of UI objects, mostly based on the object hierarchy as it appears to Orca. Added the following commands:
- Commands for moving to the parent, first child, next and previous sibling. Bound to CTRL+Orca+arrows.
- A command for acting on the current object with navigator focus, usually performs a click. Bound to CTRL+Orca+Return.
- A command for toggling the simplification of the object hierarchy. Bound to CTRL+Orca+S.