Make popup menu WCGA 2.1 compliant

[nikku]

Is your feature request related to a problem? Please describe.

Currently the popup menu is a keyboard trap that is insufficiently indicated to assistive technology (screen readers), it violates no-keyboard-trap.

Describe the solution you'd like

The popup editor is clearly indicated as a keyboard trap with ESC (cancel) or ENTER (to select action) being the two promoted navigation actions.

Describe alternatives you've considered

Do not trap TAB but instead only trap arrow keys. Tab will focus individual entries in the select, and tabbing out of the component will close it.

Additional context

Found via https://github.com/camunda/web-modeler/issues/7929#issuecomment-2003338026.

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Child of https://github.com/bpmn-io/internal-docs/issues/909

[nikku]

I added the following as an alternative, which more clearly follows existing usage patterns (and no-keyboard-trap):

Do not trap TAB but instead only trap arrow keys. Tab will focus individual entries in the select, and tabbing out of the component will close it.

[barmac]

Drop TAB makes sense to me.

[nikku]

#874 ships initial support, we'll iterate if there is more to do.