Add group labels to toolbars for acessibility
Add group labels to toolbars for acessibility

closes CORE-3131

Test Plan:
  - Enable RCE enhancements feature flag
  - Go to a page with an RCE
  - Enable screenreader and go to the toolbar
  - The toolbar groups should have labels

Change-Id: I788fe9368aadbd086eab5beb59e0120b9cdceb8c
Reviewed-on: https://gerrit.instructure.com/199356
Tested-by: Jenkins
Reviewed-by: Ryan Shaw <ea3cd978650417470535f3a4725b6b5042a6ab59@instructure.com>
QA-Review: Ryan Shaw <ea3cd978650417470535f3a4725b6b5042a6ab59@instructure.com>
Product-Review: Daniel Sasaki <ae19fabf7fe19dff310008c9b6a4d2ec84d311d8@instructure.com>

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