Make datepicker accessible

The Civi datepicker field aren't accessible which means that other than cursor actions, you can select date from calendar using control keys.

This is about making datepicker accessible and here's a working example how it will look like after completing changes- https://dequeuniversity.com/library/aria/date-pickers/sf-date-picker

A user should be able to use datepicker with the help of control keys, not just cursor actions, and tasks involved are:

1. Tab to select date input field
2. On date field select calendar dialog, focus on current or default date.
3. Tab action switches to previous/next/month/year button
4. Show a close button on down right corner that has a tabstop.
5. Left/Right/Up/Down to change day/month/year.
6. Enter to select