Reland: Add basic support for Ctrl-Z to editable TextViews

Reland 9201e797 which was reverted in
c8f08e07.

Original description:
* Add an UndoManager to the Editor for each editable TextView
* Record operations as being owned by that Editor
* Parcel the undo state
* Wire hardware keyboard shortcuts Ctrl-Z for undo and Ctrl-Shift-Z
  for redo into TextView shortcut handling.
* Expose IDs for "undo" and "redo" for symmetry with cut/copy/paste.

Additional fix:
* Ensure each UndoOwner always has a valid mManager, even after the
  UndoManager is parceled and restored.

Bug: 19332904
Bug: 19505388
Change-Id: Iad4476e6e9ca952281e69bf22c07cca915dfa7bd