Remove the JavaScript module and its logic to toggle the disabled
state on the submit button. Instead, let the browser handle this
natively by setting the `required` attribute, which naturally prevents
early submissions.
Retain the current styling for 99% of cases by using the
:required:invalid selector to target the submit button to make it
appear disabled. This slight duplication of styles is needed because,
despite the form effectively being disabled natively, the core
mediawiki-ui styles only account for :disabled on the button directly
and not e.g. inherited via form:invalid. It is also unclear whether
we would want that, since there is some value to be had from having
the form give a consistent look with a progressive button that can
be submitted even at the wrong time to yield an assistive message to
the required field, so hence handling this locally for now instead of
with a generalised approach.
In order to use the required true/false idiom, I have switched the
generating of the HTML string from the old Xml::element method
to Html::element. This means there is no need to store it in an array
first and conditionally set it since true/false will result in absence
or required="" as needed.
As side-effect from this, redundant attributes like value="" and
type="text" are ommitted from the output, just as MediaWiki core does
more generally.
Bug: T283303
Change-Id: I2c75e09dd3f89fa11fca311b4e1f8133946b01b1
