Running (custom) validators should also execute setCustomValidity on the element #16353

I'm submitting a ...

• bug report
• feature request
• other

Current behavior:
Right now, when validators run, they only set the AngularJS validity, and not the HTML validtity. Because of this, we can't use the :invalid pseudo selector, which is used by Bootstrap 4 to display the validation styling.

Expected / new behavior:
Running validators should also set the the HTML validity in order to use :invalid pseudo selector.

AngularJS version: 1.5.11 (I checked source code of the latest version on master too)

Browser: [al]

Anything else:
I don't know if PR can still be made on this. If so, I could check it out to create one.