Improve on Modal AutoFocus

Problem

In the discussion at gitlab#29012 (comment 440740184) there has been voiced the need for auto focus of modals to be more input aware instead of focusing on the first link field. This would potentially improve keyboard-only navigation of GitLab significantly when navigating modals.

The best built-in behaviour would be to ignore links element in the autofocus algorithm and focus on the first actionable element. If there are no such elements inside the modal, then the primary button at the buttom will be automatically selected (this is already the case)

Screenshot

Proposal

The discussion at gitlab#29012 (comment 442439797) indicated:

the request of making the first input (API field) the autofocus point is the correct behavior 🎉 (validated with W3)