theme editor errors work with screenreader
theme editor errors work with screenreader

fixes CNVS-22149
fixes CNVS-22150

test plan:
  - go to theme editor with a screenreader
  - input an invalid color
  - when the red error box pops up the
    screenreader reads that the color
    is invalid
  - red error boxes are tabbable
    (though you'll skip past them at
     first, you can tab back)

Change-Id: I84a33a35039fdc064ba2dc51005d777851c493ee
Reviewed-on: https://gerrit.instructure.com/59484
Reviewed-by: Jacob Fugal <f862f167b85d41b225785c70d70808bc7337c1fe@instructure.com>
QA-Review: Nathan Rogowski <2e8aa918660411855c6d44d5bb2da677aa033255@instructure.com>
Tested-by: Jenkins
Product-Review: Aaron Cannon <25919c673621c006b735dcd5a28df63325948e2b@instructure.com>

jay3126/canvas-lms,fronteerio/canvas-lms,sdeleon28/canvas-lms,whalejasmine/canvas-lms,sdeleon28/canvas-lms,utkarshx/canvas-lms,tgroshon/canvas-lms,greyhwndz/canvas-lms,tgroshon/canvas-lms,antoniuslin/canvas-lms,jay3126/canvas-lms,SwinburneOnline/canvas-lms,sfu/canvas-lms,leftplusrightllc/canvas-lms,utkarshx/canvas-lms,efrj/canvas-lms,utkarshx/canvas-lms,greyhwndz/canvas-lms,Rvor/canvas-lms,sfu/canvas-lms,skmezanul/canvas-lms,jay3126/canvas-lms,whalejasmine/canvas-lms,Jyaasa/canvas-lms,grahamb/canvas-lms,HotChalk/canvas-lms,tgroshon/canvas-lms,Rvor/canvas-lms,kyroskoh/canvas-lms,grahamb/canvas-lms,antoniuslin/canvas-lms,antoniuslin/canvas-lms,djbender/canvas-lms,juoni/canvas-lms,juoni/canvas-lms,Jyaasa/canvas-lms,skmezanul/canvas-lms,grahamb/canvas-lms,kyroskoh/canvas-lms,whalejasmine/canvas-lms,redconfetti/canvas-lms,HotChalk/canvas-lms,leftplusrightllc/canvas-lms,djbender/canvas-lms,skmezanul/canvas-lms,juoni/canvas-lms,skmezanul/canvas-lms,fronteerio/canvas-lms,HotChalk/canvas-lms,djbender/canvas-lms,leftplusrightllc/canvas-lms,sdeleon28/canvas-lms,redconfetti/canvas-lms,efrj/canvas-lms,Rvor/canvas-lms,grahamb/canvas-lms,Rvor/canvas-lms,kyroskoh/canvas-lms,grahamb/canvas-lms,SwinburneOnline/canvas-lms,SwinburneOnline/canvas-lms,fronteerio/canvas-lms,Jyaasa/canvas-lms,efrj/canvas-lms,whalejasmine/canvas-lms,SwinburneOnline/canvas-lms,jay3126/canvas-lms,tgroshon/canvas-lms,greyhwndz/canvas-lms,roxolan/canvas-lms,redconfetti/canvas-lms,sdeleon28/canvas-lms,venturehive/canvas-lms,kyroskoh/canvas-lms,sfu/canvas-lms,utkarshx/canvas-lms,roxolan/canvas-lms,venturehive/canvas-lms,venturehive/canvas-lms,sfu/canvas-lms,fronteerio/canvas-lms,antoniuslin/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,redconfetti/canvas-lms,HotChalk/canvas-lms,venturehive/canvas-lms,djbender/canvas-lms,leftplusrightllc/canvas-lms,efrj/canvas-lms,roxolan/canvas-lms,juoni/canvas-lms,roxolan/canvas-lms,greyhwndz/canvas-lms,Jyaasa/canvas-lms