Add support for aria-disabled attribute

[rlaffers]

What:

Adding support for aria-disabled attribute in toBeDisabled and toBeEnabled matchers.

Why:

aria-disabled is a standard attribute with semantics similar to the disabled attribute. Until now, this attribute has been ignored by toBeDisabled and toBeEnabled matchers.

How:

By extending toBeDisabled and toBeEnabled matchers.

Checklist:

• Documentation
• Tests
• Updated Type Definitions N/A
• Ready to be merged

[eps1lon]

This was discussed at length in #144. Could you continue the discussion there? If you want to propose an implementation please address all the points raised in #144.

[gnapse]

I'll add a note in the README to the documentation of these matchers.

[gnapse]

Please check #303.

[rlaffers]

Thanks for pointing out the discussion in #144 . (I had not come across it although I searched for issues mentioning toBeDisabled; only open issues though). The reasoning for not adding this to toBeDisabled is sound and I agree with it. I'm closing this PR.