fix media track/caption XSS vulnerability, fixes CNVS-17659
fix media track/caption XSS vulnerability, fixes CNVS-17659

ensure locale and other fields are properly sanitized when building
<track /> tags

test plan: see repro steps on CNVS-17659

Change-Id: I8016d05ce12854166ed467f06a2769c5f1bfa979
Reviewed-on: https://gerrit.instructure.com/46288
Tested-by: Jenkins <d95b56ce41a2e1ac4cecdd398defd7414407cc08@instructure.com>
Reviewed-by: Cody Cutrer <c4fe2b1d90ef8f2548c8aeabfa633434316f0305@instructure.com>
QA-Review: Caleb Guanzon <54fa1f30d451e4f3c341a8f3c47c9215fd0be9c6@instructure.com>
Product-Review: Jon Jensen <44f878afe53efc66b76772bd845eb65944ed8232@instructure.com>

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