Add live region info to default tool alerts
Add live region info to default tool alerts

Closes PLAT-4813

Test Plan:
- Configure a default tool and navigate to the assignment create
  UI.
- Return some content from the default tool
- Verify the "success" notification is announced in a screen
  reader

Change-Id: Ia713945de77251c85a3e50dd554aa938bf95e893
Reviewed-on: https://gerrit.instructure.com/206087
Reviewed-by: Tucker Mcknight <4b51b98c1d84aa97854d216bd061ce5d3eda8a28@instructure.com>
QA-Review: Tucker Mcknight <4b51b98c1d84aa97854d216bd061ce5d3eda8a28@instructure.com>
Tested-by: Jenkins
Product-Review: Weston Dransfield <e9203059795dc94e28a8831c65eb7869e818825e@instructure.com>

sfu/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,sfu/canvas-lms