fix webkit focus outline for screenreader-only elements
fix webkit focus outline for screenreader-only elements

fixes CNVS-12480

test plan:
  * open a discussions index page in Chrome or Safari
  * click to collapse "Pinned Discussions"
  * verify that the focus outline wraps the heading reasonably

Change-Id: I3b0f118ba9ab310ad1d9295395704f30d8dc96be
Reviewed-on: https://gerrit.instructure.com/33400
Tested-by: Jenkins <d95b56ce41a2e1ac4cecdd398defd7414407cc08@instructure.com>
Reviewed-by: Ryan Florence <2d8900489f91ac272fd9ce9d5789db6522668ca2@instructure.com>
QA-Review: Trevor deHaan <85df72112e8a9484fec7b3db2e31789c2c2d4e07@instructure.com>
Product-Review: Braden Anderson <a6cc2cef7d25f27847876bdb81651755fcebacf0@instructure.com>

instructure/canvas-lms,kyroskoh/canvas-lms,gbleydon/canvas-lms,fronteerio/canvas-lms,Unow/canvas-lms,juoni/canvas-lms,Rvor/canvas-lms,venturehive/canvas-lms,Rvor/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,roxolan/canvas-lms,tgroshon/canvas-lms,ShreniiNepal/shrenii_lmp,gbleydon/canvas-lms,antoniuslin/canvas-lms,juoni/canvas-lms,grahamb/canvas-lms,greyhwndz/canvas-lms,dgynn/canvas-lms,efrj/canvas-lms,roxolan/canvas-lms,sdeleon28/canvas-lms,jay3126/canvas-lms,fronteerio/canvas-lms,samuels410/greatlakes-lms,greyhwndz/canvas-lms,eCNAP/CANVAS,eCNAP/CANVAS,whalejasmine/canvas-lms,utkarshx/canvas-lms,kyroskoh/canvas-lms,fronteerio/canvas-lms,va7map/canvas-lms,utkarshx/canvas-lms,instructure/canvas-lms,HotChalk/canvas-lms,wrdsb/canvas-lms,SwinburneOnline/canvas-lms,redconfetti/canvas-lms,wrdsb/canvas-lms,narigone/canvas,tgroshon/canvas-lms,matematikk-mooc/canvas-lms,skmezanul/canvas-lms,snehakachroo1/LSI_replica,sfu/canvas-lms,sfu/canvas-lms,narigone/canvas,djbender/canvas-lms,samuels410/greatlakes-lms,juoni/canvas-lms,usmschuck/canvas,shidao-fm/canvas-lms,samuels410/greatlakes-lms,greyhwndz/canvas-lms,jay3126/canvas-lms,ShreniiNepal/shrenii_lmp,wye0220/shindig-canvas,sfu/canvas-lms,whalejasmine/canvas-lms,HotChalk/canvas-lms,shidao-fm/canvas-lms,Rvor/canvas-lms,tgroshon/canvas-lms,AndranikMarkosyan/lms,sdeleon28/canvas-lms,eCNAP/CANVAS,va7map/canvas-lms,skmezanul/canvas-lms,djbender/canvas-lms,Jyaasa/canvas-lms,efrj/canvas-lms,grahamb/canvas-lms,venturehive/canvas-lms,kyroskoh/canvas-lms,instructure/canvas-lms,eCNAP/CANVAS,sdeleon28/canvas-lms,sdeleon28/canvas-lms,skmezanul/canvas-lms,djbender/canvas-lms,gbleydon/canvas-lms,Jyaasa/canvas-lms,roxolan/canvas-lms,djbender/canvas-lms,HotChalk/canvas-lms,Unow/canvas-lms,snehakachroo1/LSI_replica,redconfetti/canvas-lms,greyhwndz/canvas-lms,dgynn/canvas-lms,venturehive/canvas-lms,leftplusrightllc/canvas-lms,va7map/canvas-lms,efrj/canvas-lms,grahamb/canvas-lms,matematikk-mooc/canvas-lms,shidao-fm/canvas-lms,redconfetti/canvas-lms,usmschuck/canvas,grahamb/canvas-lms,AndranikMarkosyan/lms,leftplusrightllc/canvas-lms,roxolan/canvas-lms,snehakachroo1/LSI_replica,venturehive/canvas-lms,shidao-fm/canvas-lms,skmezanul/canvas-lms,SwinburneOnline/canvas-lms,Unow/canvas-lms,fronteerio/canvas-lms,efrj/canvas-lms,ShreniiNepal/shrenii_lmp,dgynn/canvas-lms,instructure/canvas-lms,narigone/canvas,redconfetti/canvas-lms,wrdsb/canvas-lms,HotChalk/canvas-lms,AndranikMarkosyan/lms,SwinburneOnline/canvas-lms,usmschuck/canvas,whalejasmine/canvas-lms,instructure/canvas-lms,jay3126/canvas-lms,whalejasmine/canvas-lms,instructure/canvas-lms,antoniuslin/canvas-lms,sfu/canvas-lms,va7map/canvas-lms,SwinburneOnline/canvas-lms,grahamb/canvas-lms,utkarshx/canvas-lms,dgynn/canvas-lms,kyroskoh/canvas-lms,usmschuck/canvas,snehakachroo1/LSI_replica,sfu/canvas-lms,narigone/canvas,Rvor/canvas-lms,juoni/canvas-lms,Jyaasa/canvas-lms,tgroshon/canvas-lms,samuels410/greatlakes-lms,leftplusrightllc/canvas-lms,instructure/canvas-lms,utkarshx/canvas-lms,matematikk-mooc/canvas-lms,wrdsb/canvas-lms,AndranikMarkosyan/lms,jay3126/canvas-lms,matematikk-mooc/canvas-lms,wye0220/shindig-canvas,Jyaasa/canvas-lms,antoniuslin/canvas-lms,wye0220/shindig-canvas,leftplusrightllc/canvas-lms,antoniuslin/canvas-lms,ShreniiNepal/shrenii_lmp