Should store per-interpolation-batch surjectivity information

[inducer]

In the (relatively common) surjective case, we could skip emitting these global barriers:

meshmode/meshmode/discretization/connection/direct.py

Lines 310 to 311 in cdcc7f5

	result[iel_init, idof_init] = 0 {id=init}
	... gbarrier {id=barrier, dep=init}

)

meshmode/meshmode/discretization/connection/direct.py

Lines 342 to 343 in cdcc7f5

	result[iel_init, idof_init] = 0 {id=init}
	... gbarrier {id=barrier, dep=init}

I noticed this while reviewing #192.

cc @thomasgibson