[Meta] Improve the accessibility of the Smart Date module

@simohell thank you for the feedback. The Smart Date widget has been tested for accessibility before, but of course the field is always evolving.

For each of the identified issues, would it be possible to have additional detail (ideally with a screen grab or highlighted code) on where the issue is exactly. A proposed fix would be ideal as well, or even a link to some documentation that discusses possible remediation approaches.

Added the first child issue. I thing I could discuss the input-field order at Core UX weekly, since it's a little bit complex. Hiding and showing fields dynamically is sometimes a bit hard to do well. We don't want to move things too much but also to add new items in the correct place.

If there is some background information on how the current implementation was decided on, it would be helpful.