extract canvas_ext gem

fixes: CNVS-11902

Test Plan:

Make sure Canvas is not broken.  This will break a lot of things if it
does not work correctly.

Change-Id: I8701ff8c271a162a712fe3be05a4fd361430b26e
Reviewed-on: https://gerrit.instructure.com/32113
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jacob Fugal <jacob@instructure.com>
QA-Review: Jeremy Putnam <jeremyp@instructure.com>
Product-Review: Jason Madsen <jmadsen@instructure.com>