_disableAccessibleState property needs documenting & adding to .schema files

[moloko]

it's been added to component.model.schema (in v4) but I think it needs to be added to more than just that.

[moloko]

as mentioned in the accessibility chat it might be of more use to drop _disableAccessibleState in favour of _isA11yComponentDescriptionEnabled (and add that to the .schema files)

[moloko]

as mentioned in the accessibility chat it might be of more use to drop _disableAccessibleState in favour of _isA11yComponentDescriptionEnabled (and add that to the .schema files)

Whichever we do go with, I think it would be an idea to turn off the 'heading ARIA completion' for non-interactive components like adapt-contrib-text and adapt-contrib-graphic. As these components mark as completed as soon as they are 'in view' it seems odd/confusing to tell a screenreader user that they are complete before they've actually read through them properly.

[chris-steele]

@oliverfoster if this is still required I can look at what this property means and document it

[oliverfoster]

removed in #247