mro_package_moved must act on all effective names

mro_package_moved must act on all effective names

See the test case in the commit. It passes in 5.8.x and blead (as of
this commit), but not 5.10-5.13.7.

In every case the name to be passed to mro_gather_and_rename is cre-
ated using an SV, so we might as well pass that instead of extracting
the char array and length from it.

That allows us to pass an AV instead, if there are multiple names to
take into account.