ve.ui.MWTitleInputWidget: Restore 've-ui-mwTitleInputWidget' CSS class

've-ui-mwTitleInputWidget-menu', too. Removed in
b3d2e9013feb283b6b531dc6383d5664d9a97b17, but we actually
use these classes in styles and in browser tests.

Bug: T101600
Change-Id: I40dae9c68bbcba2f980c307fe0dfa0956b4eb78a