Make edit popover accessibile

[panphora]

The default Remake edit popover (that pops up when clicking an element with an edit: attribute) isn't accessible by default.

It should have ARIA tags automatically generated for the clickable element as well as the popover. See:

• https://developers.google.com/web/fundamentals/accessibility/semantics-aria
• https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/Roles/dialog_role