Give screenreader indication to speedgrader for mod grading
Give screenreader indication to speedgrader for mod grading

fixes CNVS-25128

Test Plan:
  - Set up everything for moderated grading
  - Go to speedgrader
  - select a grade to be the selected grade
  - Screenreaders should pick up a message indicating
    that the grade with the checkbox is the chosen grade

Change-Id: Ifc3281e453221630bc47076b22898fb14c853692
Reviewed-on: https://gerrit.instructure.com/67603
Reviewed-by: Jeremy Stanley <b3f594e10a9edcf5413cf1190121d45078c62290@instructure.com>
Tested-by: Jenkins
QA-Review: Jahnavi Yetukuri <ed2b2672ccc2e59e56c0615df7f01b579202e014@instructure.com>
Product-Review: Clay Diffrient <9dff2e5c98626d20d2848250c411e8009465bb87@instructure.com>

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