Move it to its own module mediawiki.widgets.UserInputWidget. It's
currently used in HTMLUserTextField only.
Bug: T108733
Change-Id: Id8c6dd5d9616086bdb0918442bfafe9ec708ab31
Can be configured with the 'ipallowed' config parameter, which defaults
to false (IP's not allowed).
Bug: T106807
Change-Id: Ib2885883bdb3383c60382bf3257afdfc3cc26821
To use OOUI for forms with user name autocomplete, the new widget
UserInputWidget interacts like the jQuery pendant (working with css
class "mw-autocomplete-user").
It is also available in HTMLForm as "user".
Example usage: Iaeff912e6437d6ebef0d5b1919ce8cf53a7fd5f1
Change-Id: I9501c85f4288c255bbe3a5284e99b57b6169916f
