Refactor NamespaceInputWidget

Refactor NamespaceInputWidget

* Refactor NamespaceInputWidget into two widgets: NamespaceInputWidget
  and ComplexNamespaceInputWidget. The former is now only the dropdown
  (and inherits from DropdownInputWidget), the latter is the dropdown
  plus two checkboxes.
* Change ComplexNamespaceInputWidget configuration to take nested config
  for `invert`, `associated`, and `namespace`, rather than require
  parameters like `invertName` and so on for every combination.
* Implement standalone JavaScript versions of both widgets (previously
  mw.widgets.NamespaceInputWidget could only be created via infusion
  of the PHP widget).

Bug: T99256
Bug: T106138
Bug: T109559
Change-Id: Ie2fee6d035339ceb934fca991675480db3d630d1