fix(action-sheet): add aria-labelledby

[averyjohnston]

Pull request checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)
  • Some docs updates need to be made in the ionic-docs repo, in a separate PR. See the contributing guide for details.
• Build (npm run build) was run locally and any changes were pushed
• Lint (npm run lint) has passed locally and any fixes were made for failures

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe): Accessibility fixes

What is the current behavior?

ion-action-sheet does not have an aria-label or aria-labelledby attribute, which his required for the dialog role.

Issue URL: N/A (internal ticket)

What is the new behavior?

• If the header property is defined, aria-labelledby is set to point to that element.
  • Note that a fallback to subHeader is not included, because if header isn't defined, the subHeader doesn't render either way due to it being wrapped in the header element.
• Duplicate role="dialog" removed, since it was causing an Axe violation due to nested dialogs.

Does this introduce a breaking change?

• Yes
• No

Other information

A separate PR will be made to document accessibility best practices with this change in mind.