Replace Media namespace redirects with File namespace

Replace Media namespace redirects with File namespace

If a user creates a redirect that goes to a [[Media:example.jpg]]
page, then an exception is thrown because NS_MEDIA is a virtual
namespace. This change catches this case and changes the namespace
to an NS_FILE namespace and the redirect works correctly. This
change only happens when we are dealing with a redirect so other
uses of the NS_MEDIA namespace shouldn't be affected.

Bug: T203942
Change-Id: Ia744059650e16510732a65d51b138b11cbd43eb4