TextView—Fix inverted movements by arrows in RTL

TextView—Fix inverted movements by arrows in RTL

Using Ctrl + left/right to skip between words, or left/right to cancel a
selection, were causing movement on the screen in the opposite direction
of the glyph on the key. This was surprising and awful UX for RTL users.

This is based on a patch covering the former case by:
Author:    Mehdi Sadeghi <mehdi@mehdix.org>
Date:      Sat Feb 18 02:16:00 2017 +0000

https://bugzilla.gnome.org/show_bug.cgi?id=136059