Convert Special:Search to OOUI

Authored by matmarex.


Convert Special:Search to OOUI

Limiting this to the primary form for now, which was using old
MediaWiki UI styles. There are some native elements tucked in the
advanced form which I am not changing here yet.

Also, use new search suggestions provided by TitleInputWidget.

Bug: T100898
Change-Id: I699cf27a686f2615a22fce70f43b9f89092485c9