The help text for datetime field needs an ID for screen readers.

Problem/Motivation

Same issue as 2126761. The datetime help text field says that it is a description field, but has no ID pointing to what it is describing.

<div class="description">Some really helpful text.</div>

This is a problem for users using a screen reader. Without a description, it is not apparent what the field is for.

To reproduce:

• add a date field to a content type
• add help text to the field.
  • e.g. for the article content type go to admin/structure/types/manage/article/fields/node.article.field_date_time
• add a node and inspect the markup for the datetime help text

Proposed resolution

• add an attributes variable to datetime-wrapper.html.twig
• include the variable in template_preprocess_datetime_wrapper()

Remaining tasks

• Create an initial patch
• find a new home