Make delete all pages button a11y friendly
Make delete all pages button a11y friendly

closes OUT-3807

flag=bulk_delete_pages

test-plan:
- ensure VO announces the bulk delete pages button as dimmed
when the button is disabled

Change-Id: Ib591214fe767588868858cba7f7dcf7b45d34762
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/242408
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: Michael Brewer-Davis <785693f4c81267e5b88c0f98d39b56a39a2b6910@instructure.com>
QA-Review: Daniel Sasaki <ae19fabf7fe19dff310008c9b6a4d2ec84d311d8@instructure.com>
Product-Review: Jody Sailor

instructure/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,sfu/canvas-lms