[Meta] Improve the accessibility of the Smart Date module

Problem/Motivation

The Drupal accessibility team have been considering the imminent release of Drupal CMS and we have agreed that it would be a good idea to assess the contrib modules that are going to get into Drupal CMS for accessibility issues #3475279: [Meta] Audit each module to be included into Drupal CMS for accessibility issues.

The testing was done with Drupal CMS 1.0 using the events recipe unsing Chrome on OSX 15.2 + VoiceOver. Testing did not cover all Smart Date features. Testing was done for the event default date field, a date field allowing multiple date ranges with date only and a single date range field with time and date.

It should be noted that on default date input on Chrome + VoiceOver reads the default values dd.mm.yyyy incorrectly as percentages. This will not be fixed in Drupal but in the browser https://issues.chromium.org/issues/361250561

Remaining tasks

• Create detailed issues on the findings
• Error messages are not announced, on error focus is set on an empty. Error message can appear visually 3 times in a field (wcag 3.3.1)
• Error message is not shown in context and is vague (wcag 3.3.3)
• #3502468: Keyboard navigation does not follow visual order of items (wcag 2.4.3)
• Input values may add or hide input elements (wcag 3.2.2)
• #3502482: Focus indicator is partially blocked by next input element. This is not a wcag violation, but fixing this is easy and recommended by the accessibility team.
• #3502478: Typing in a 5+ figure year to an empty date field results in inconsistent behaviour (maybe wcag 3.2.2)