extract GB2 keyboard nav and allow it to be i18nd

fixes CNVS-13044

Previously we were comparing to a specific character code that wasn’t
subject to i18n so when the translators got into the translations the
shortcuts would have been all messed up. Now we’re comparing strings
instead so when the key changes so does what we’re looking for. To make
this a bit easier in the future I’ve started extracting some of the
key checking logic so we can easily apply this elsewhere.

Test Plan:
- As a teacher navigate to GB2
- Use the keyboard shortcuts
  - They should still work

Change-Id: If23046c568d7a09b386c7ac8e1176192d2d96061
Reviewed-on: https://gerrit.instructure.com/35002
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Mike Nomitch <mnomitch@instructure.com>
Reviewed-by: Liz Abinante <labinante@instructure.com>
QA-Review: Amber Taniuchi <amber@instructure.com>
Product-Review: Simon Williams <simon@instructure.com>