[meta] Improve the accessibility of the autosave_form 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.

Remaining tasks

• #3368261: Non-visible buttons are still tabbable and read out by screenreaders