Gtk input controls feature visual cursor movement, where the cursor disregards
the logical order of the characters. However, Ctrl-Arrow accelerators, which
jump over words rather than characters, move the cursor logically, which is very
confusing in RTL paragraphs.

On Windows, where the arrows move the cursor logically, they simply flip the
arrows for both by-character and by-word movement. However, we'll have to do
something more complicated: make by-word movement visual as well.