VO+Safari: arrow-navigation to answer comments

I can't really say this is a fix.. it's a hack at best, so I scoped it
to Safari. It also introduces a new issue which I wasn't able to solve:

Anytime you focus *out* of the comment editor using VO+arrow, you can no
longer reach the editor using arrows, only using TAB. BUT, if you use
TAB to focus-out of the editor, using arrows just keeps working! Crazy,
lame, and I don't have a clue what's going on.

Closes CNVS-15099

TEST PLAN
---- ----

  - using Safari, create a quiz with a single multiple-choice question
  - turn on VoiceOver and edit the quiz
  - edit the question
    + keep using VO+RIGHT until you reach the input field for the
      first answer
    + now press VO+RIGHT again
      - verify that in about half a second, your focus is shifted to the
        comment editor and you hear "Comments, if the user chooses this
        answer"
    + shift+TAB, you're now back onto the input field, then TAB:
      - you should, again, see the comment editor
    + shift+TAB, then VO+RIGHT
      - again, you see the comment editor
    + now press VO+RIGHT, your focus shifts to the little edit icon
      - try using VO+LEFT to go back to the comment editor, and notice
        how it doesn't; instead it takes you to the input field, and
        it seems we are never able to access the comment editor
        anymore using VO+arrows

Change-Id: I52df20387d2d2d2126112448b5a992c70e8d2272
Reviewed-on: https://gerrit.instructure.com/41600
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Trevor deHaan <tdehaan@instructure.com>
Reviewed-by: Brian Finney <bfinney@instructure.com>
Reviewed-by: Derek DeVries <ddevries@instructure.com>
Product-Review: Ahmad Amireh <ahmad@instructure.com>