Selectors should recognise aria-label and aria-labelled-by where appropriate

[timhunt]

The selectors defined in https://github.com/minkphp/Mink/blob/master/src/Selector/NamedSelector.php do a good job of recognising most HTML. E.g. they will find a checkbox by the associated , or a link but the alt text of the icon inside the .

However, at present they do not find e.g. , or using aria-labelled-by="id" on the checkbox, rather than for="id" on the label. It would be nice to fix this.

(This is something we would like in the Moodle project. See https://tracker.moodle.org/browse/MDL-65940.)

[bkosborne]

Created a PR that adds this support for buttons at least.