Add aria labels and enable accessibility support in editor

What does this MR do and why?

Monaco editor wiki states:

You can toggle the trapping of Tab with Ctrl+M on Windows and Linux and with Ctrl+Shift+M on OSX, and subsequent Tab keys will move focus out of the editor.

After testing in multiple editors, I can confirm it is working as intended in our implementations. This MR adds the required role, aria labels, and an aria-live region to communicate the editor's state and built-in functionality to navigate around tab trapping.

References

Please include cross links to any resources that are relevant to this MR. This will give reviewers and future readers helpful context to give an efficient review of the changes introduced.

• Monaco editor tab trapping docs
• Accessibility Audit Issue

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

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CleanShot_2025-01-28_at_16.20.10.mp4

Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Related to https://gitlab.com/gitlab-org/gitlab/-/issues/511809