Also replace many instances of GetElementTransformation(0) with
GetTypicalElementTransformation() and instances of GetElementGeometry(0) with
GetTypicalElementGeometry().

Remove some "early returns" in PA code with empty partitions. The reasoning is
that the early returns create divergent code paths among different MPI ranks,
which can cause deadlocks if e.g. collectives are used in code paths on not all
ranks.

Analogous to Mesh::GetTypicalElementGeometry

…try()

…ElementGeometry

This is a variable-order version of TraceFiniteElementForGeometry, analogous to
FiniteElementCollection::GetFE, which is a variable-order version of
FiniteElementForGeometry.