Apply and use data-drupal-selector consistently.

Problem/Motivation

#1305882: drupal_html_id() considered harmful; remove ajax_html_ids to use GET (not POST) AJAX requests → adds data-drupal-selector to wean us off targeting IDs with JavaScript.

However this not applied to all form elements.

Proposed resolution

Add it to at least the following elements:

• Radios
• Checkboxes
• Date elements
• potentially more ...

Remaining tasks

Revive parts of the more complete patches from #1305882: drupal_html_id() considered harmful; remove ajax_html_ids to use GET (not POST) AJAX requests → and continue from there.

User interface changes

API changes

Data model changes