Html: Make addition of 'mw-ui-input' conditional on $wgUseMediaWikiUIEverywhere

Html: Make addition of 'mw-ui-input' conditional on $wgUseMediaWikiUIEverywhere

We were always adding it previously, which seemed harmless since
'mediawiki.ui.input' RL module, providing the styling, was only loaded
if $wgUseMediaWikiUIEverywhere was true… unless someone loaded it
manually to have specific input fields styled. Whoops.

There are a lot more unconditional additions like this in tons of
places in the code, and someone should check whether each one is
intentional or not, but probably no one will. Oh well.

Bug: T92496
Change-Id: I5e91a3852a76ebbbfe64485bccb4c30ddee28b66