Steps to replicate the issue

• Go to Special:CiteThisPage or Special:WhatLinksHere
• try typing in some names of pages
• It autocompletes the names of the pages.
• Note the behaviour

• Go to Special:Delete, Special:EditPage, Special:PageHistory, Special:PageInfo or Special:Purge
• Start typing the name of a page

What happens?:

There is no autocomplete for these special pages

What should have happened instead?:

There should be autocompletion for these special pages.

Software version:

Tested on 1.43

Notes

These should use the same title input widget (includes/Widget/TitleInputWidget.php) if they don't already.
includes/HTMLForm/Field/HTMLTitleTextField.php is probably relevant as well (sorry for the poor notes, but I figured some hints are better than nothing).