Review deprecation processes for ARIA attributes (and roles?)

[smhigley]

Semi-related to #1862

We have logic in aria.js to apply ARIA 1.2-specific deprecation warnings, but no other built-in deprecation language or system, particularly for deprecating support for an attribute on a role rather than deprecating the entire attribute/role.

TODOs:

• Figure out anything we need to do to align with other specs
• Set specific requirements around what should be deprecated vs. just removed
• Set wording/formatting for deprecation notice
• Add script for inserting the deprecation wording?

[jnurthen]

Discussed at ARIA meeting - https://www.w3.org/2023/02/02-aria-minutes#t05

[pkra]

Related: #80 asking if role=presentation should be deprecated. Though the minutes linked above mention that the group decided against deprecation (and for synonyms).