Consider allowing aria-valuetext for combobox role

[scottaohara]

In attempting to decide upon a way for the customizable select element to calculate the value to expose to users, use cases arose where allowing an author to set aria-valuetext on the select element (role=comobox) instead of having to fiddle with the returned markup from the select element's chosen option, seemed like a good idea.

Consider the following:

<!-- this option was specifically marked up so that the value would be "smile icon 1" rather than something like "smile smile icon 1" -->
<option>
  <span role=img aria-label="smile icon 1">🙂</span>
  <span class=description aria-hidden=true>smile icon 1</span>
</option>

In the collapsed state, the description is set to display none so that only the emoji is displayed.

The following is a lot easier for a developer to do to get the option to announce in the intended way - but the returned content to the selectedoption element will only be the emoji, not the aria-label

<option aria-label="smile icon 1">🙂</option>

so, if someone could do

<select aria-valuetext="smile icon 1">
  <button><selectedcontent>🙂</selectedcontent></button>
  ...
</select>

that'd be a lot nicer than having to fiddle with very specific markup patterns, ensuring that every bit was marked up properly to convey the intended value when interacting with the collapsed select and when reviewing individual options.

cc @smhigley @aleventhal

[spectranaut]

We should find the existing issues related to aria-valuetext before discussing this in a meeting.

[scottaohara]

#711