Add `enterkeyhint` attribute ("Enter Key Hint")

[Schweinepriester]

• Spec: https://html.spec.whatwg.org/multipage/interaction.html#input-modalities:-the-enterkeyhint-attribute

• Chrome 77+: https://www.chromestatus.com/feature/5654529808793600

• iOS 13.4: https://webkit.org/blog/10247/new-webkit-features-in-safari-13-1/

  On iOS, WebKit supports the enterkeyhint attribute that allows a content author to provide a label for the enter key on virtual keyboards with values for: enter, done, go, next, previous, search, and send.

• https://trac.webkit.org/changeset/251720/webkit

• https://bugzilla.mozilla.org/show_bug.cgi?id=1490661

[Schweinepriester]

https://caniuse.com/?search=enterkeyhint

• https://caniuse.com/mdn-api_htmlelement_enterkeyhint
• https://caniuse.com/#feat=mdn-html_global_attributes_enterkeyhint