The namespace change avoids a conflict with the existing Parsoid
implementation in Wikimedia\Parsoid\Ext\Cite and matches the current
Cite codebase better. We also need to add some phan stubs to allow
Cite to use Parsoid's generic DOM implementation classes, and some
type assertions to satisfy phan.
Bug: T354215
Change-Id: Ic904601b29555c9485a804f131061f207970ddd4
