Make make_opposite_face_connection work in 1D
This is needed to make grudge!48 (merged) work.
There were just a few places that needed changes:
- in
_make_cross_face_batches
: just special case the 1D case since it's ridiculously simple - in
InterpolatoryQuadratureSimplexElementGroup
: add a 0D case which returns an empty array, but makes things not complain