Add missing/invalid value defaults to attribute characteristics tables

[rahimabdi]

Describe the change

During the June 27 2024 "undefined" deep dive discussion, @cookiecrook proposed (ostensibly with WG agreement) expanding every ARIA attribute's characteristics table to include a value for both missing value default and invalid value default. Some states/properties specify an "Implicit Value for Role" which is the missing value default; note that the missing/invalid value defaults don't reflect to IDL as specified for implicit value in the characteristics tables (see 6.3.2 IDL reflection of ARIA attributes).

Per @jnurthen, the table in section 9. Handling Author errors should not be removed because validators rely on it to surface author errors.

Link to the version of the specification or documentation you were looking at

Link to documentation: https://w3c.github.io/aria

Does the issue exists in the editors draft (the editors draft is the most recent draft of the specification)?

Yes.

[keithamus]

Related: #1110

[rahimabdi]

Also related: #1895

[spectranaut]

The issue I marked as a duplicate was discussed in today's meeting, and here are the notes: https://www.w3.org/2024/07/25-aria-minutes.html#t05