OPTGROUP label is not readable on every OPTION

[Cezary Tomczyk]

Overview: VoiceOver doesn't read OPTGROUP label when the user navigates to the OPTION inside OPTGROUP.

Technical details:

- macOS Sierra 10.12.6 (16G29)
- Safari 10.1.2 (12603.3.8)

Current behaviour:

To group OPTIONS together the OPTGROUP (with label) element can be used with the related OPTION elements inside that element.

Example:

<select>
<optgroup label="Cars">
<option value="a">Name A</option>
<option value="b">Name B</option>
</optgroup>

When the user navigates through elements then the VoiceOver reads it as follows:

1. Cars, dimmed.
2. Name A.
3. Name B

Expected behaviour:

1. Cars, group.
2. Name A, group Cars.
3. Name B, group Cars.

I couldn't find any specification how this should behave, but it seems that it should work in a similar way as FIELDSET in a FORM.

[Radar WebKit Bug Importer]

<rdar://problem/34008895>