Redundant aural interface and the general interaction with CKEditor toolbar configuration

Problem/Motivation

• Active button is prepended to every description in the aural interface that is announced for every icon in the toolbar tray - that kind of redundancy should be avoided. (check available_button_redundancy.mp4)
• Keyboard users have the following feedback in the description: Buttons may be moved with the mouse or keyboard arrow keys., screenreader users instead get clear instructions to use the arrow down while in the list of available icons and within the active toolbar tray to use arrow left and right to adjust the position and arrow up to remove the icon. (check toolbar_config_instructions.mp4)
• As soon as the position of one icon is altered by a keyboard interaction the focus changes back to the first icon in the list of available buttons. (SC3.2.1 - check toolbar_config_focus_change.mp4)

Discussed and iterated on the issue with @mgifford, @the_g_bomb, @katannshaw, and @drupa11y

Steps to reproduce

• Edit a text format on admin/config/content/formats/manage/content_format?destination=/admin/config/content/formats and inspect the aural interface of the toolbar configuration fieldset on the page

Proposed resolution

• Even though it is a good thing to provide context for screen reader use, it would be preferable to front-load the unique detail and to append the more general bit at the end. That way screenreader users are able to jump off as soon as they have enough information, and in case they forget the general context due to a small working memory (active button in this case), they can still keep on listening to the entire announcement.
• Add more specific instructions to the help text in regard to the keyboard interaction with arrow up and down as well as the repositioning of icons with arrow left and right.
• Don't change the focus after altering the position of an icon after one single keyboard interaction. It is particularly problematic when trying to rearrange an icon, since after you have changed the position by one step you have to get back to the icon you were in the process of repositioning. While moving one icon in and out of the tray repositioning the focus might have a certain convenience, but still if you want to add or remove several icons in a row it might become annoying as well. So better don't intervene in the focus state after any of the arrow keys is being pressed.

Remaining tasks

User interface changes

API changes

Data model changes