Give EagerTensor a fully qualified name so __module__ doesn't generate an error

This code still differs between py2 and py3 (__module__ returns
"__builtin__" in py2, and the correct value in py3) - but its strictly better
than before since earlier it would differ between py2 and py3 and generate an
error in py3. We don't seem to correctly initialize the tp_dict in py2, so even
when passing the correct, fully qualified name, we get back "__builtin__".

Fixes #20701

PiperOrigin-RevId: 204762170