Remove support for disabled links

[paulrobertlloyd]

Description

Removes support for disabled links, which are not really a thing (or at least, shouldn’t be).

• Removes support in button Nunjucks macro for adding aria-disabled="true" if element is a and disabled is true
• Removes nhsuk-button--disabled modifier; buttons are styled as disabled if they have the disabled attribute applied
• Uses the disabled boolean attribute (as opposed to disabled="disabled"

Checklist

• Tested against our testing policy (Resolution, Browser & Accessibility)
• Follows our coding standards and style guide
• CHANGELOG entry

[frankieroberto]

Makes sense to me. 👍

A breaking change so not sure when it should get merged. @anandamaryon1?

[anandamaryon1]

Note to self: update this (now incorrect) guidance on the button page:

Disabled buttons
Disabled buttons have poor contrast and can confuse some users. Only use them if user research shows it makes things easier for users to understand.
We have developed disabled versions of the 3 buttons but we haven't tested them yet. You can get the latest disabled button code in the NHS.UK frontend library in GitHub.

[frankieroberto]

Note to self: update this (now incorrect) guidance on the button page:

Disabled buttons
Disabled buttons have poor contrast and can confuse some users. Only use them if user research shows it makes things easier for users to understand.
We have developed disabled versions of the 3 buttons but we haven't tested them yet. You can get the latest disabled button code in the NHS.UK frontend library in GitHub.

@anandamaryon1 I think this guidance would still stand (unless you have any more recent research?) but with the caveat that only disabled actual <button>s are supported, and links styled as disabled buttons aren’t supported? But possibly that’s such a weird use-case that it doesn’t need to be spelled out?