E-mail validation: RFC 6532 violation

[rutek]

E-mail input validation described in current HTML spec https://html.spec.whatwg.org/multipage/input.html#e-mail-state-(type=email) violates RFC 6532 which allows people to use diacritics in local-part of e-mail.

E-mail marked as invalid as result of current HTML spec: exampleś@example.com. It'is valid since 5 years and some e-mail providers already allow to create such accounts but browsers implementing only whatwg/html spec won't allow to use it in input type="email" (will mark it as invalid).

Browser status:
Firefox: https://bugzilla.mozilla.org/show_bug.cgi?id=1642897 rejected as their base spec is current repository
Chromium: https://bugs.chromium.org/p/chromium/issues/detail?id=1090678#c2 accepted, target version: 85

[annevk]

This is already tracked in #4562.