added remaining mypy annotation to pip._internal.locations
added remaining mypy annotation to pip._internal.locations

xavfernandez/pip,rouge8/pip,xavfernandez/pip,rouge8/pip,xavfernandez/pip,sbidoul/pip,pfmoore/pip,pypa/pip,pradyunsg/pip,pfmoore/pip,rouge8/pip,sbidoul/pip,pradyunsg/pip,pypa/pip