Update link to HTML spec from WCAG section 7

[plannero]

The deep link HTML 5.2 Autofill field section meant to reference the table containing autofill values (with examples) from section 7 of WCAG (both WCAG 2.1 and 2.2) is now redirecting to another url, which does not have a "#sec-autofill" destination.

So the link is much less useful now.

I believe the link should be changed to https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#autofill-field