Expose toggle buttons in accessibility tree

[Comandeer]

Type of report

Feature request

Provide description of the new feature

There are many toggle buttons inside editor's toolbar, e.g. "Bold", "Italic", "Underline" etc. To correctly expose them as toggle buttons in a11y tree, they must have [role=button] and [aria-pressed] attribute.

Default state:

<a href="#" role="button" aria-pressed="false">Bold</a>

Toggled/pressed state:

<a href="#" role="button" aria-pressed="true">Bold</a>

However we don't add [aria-pressed=false] for not-pressed buttons, as we do not distinguish between ordinary buttons and toggle ones. We only add [aria-pressed=true] when toggle buttons are activated. We could introduce the new toggle button category, which will always have [aria-pressed] attribute, removing handling of this attribute from ordinary buttons at the same time.

[CKEditorBot]

Closed in #5123