ComboboxControl: Use Proposed ARIA 1.2 spec for Combobox Markup

[jeryj]

The ComboboxControl created in #19657 uses the ARIA 1.1 spec, as it is the current accepted spec.

The specs for the combobox are changing quickly. Unfortunately, 1.1 was proved to be a buggy release, and they're ditching this implementation. AFAIK, only one screen reader (NVDA) even implemented this spec.

Even though 1.2 is in working draft, because it lines up so much to 1.0 and how OS-level comboboxes work, it appears that the 1.2 proposed spec is more supported out-of-the-box right now than 1.1. From Sarah Higley's article on their testing the editable combobox:

Of the two semantic variations tested, the ARIA 1.2 pattern was less buggy across the board compared to the ARIA 1.1 pattern. Assuming the version in the working draft becomes a W3C recommendation, it seems to be the clear choice for combobox markup going forward.

IMO, since hardly any screen readers have supported 1.1, it seems better to go with the proposed 1.2 spec, since it's already supported better than 1.1 just due to it working more inline with what screen readers expect. In the article linked above though, Higley says:

Of the two semantic variations tested, the ARIA 1.2 pattern was less buggy across the board compared to the ARIA 1.1 pattern.