Group special spaces and double/swapped spaces in undo mode

This introduces an elementary undo facility that accounts
for magic space, strong space, double space and its cancelling,
and swapped punctuation and its cancelling.
The former three were existing behavior ; this change adds
the swapped punctuation cancelling behavior.

Bug: 5454442
Change-Id: I87af633f30caa2788e9af725e556a7f0746d9a14