Adapt Firedrake interop to Firedrake complex branch

[inducer]

meshmode/meshmode/interop/firedrake/connection.py

Lines 513 to 515 in 6e0dffc

	# All firedrake functions are the same dtype
	dtype = self.firedrake_fspace().mesh().coordinates.dat.data.dtype
	self._validate_field(mm_field, "mm_field", dtype=dtype)

seems to require all fields to agree with the geometry dtype, which seems overly restrictive given that, as of the complex merge, Firedrake supports complex data. Florian Bruckner reported this on Slack, with a backtrace like the following:

doublelayer_sphere.py:4: DeprecationWarning: meshmode.array_context is deprecated. Import this functionality from the arraycontext top-level package instead. This shim will remain working until 2022.
  from meshmode.array_context import PyOpenCLArrayContext
/firedrake/src/pytential/pytential/symbolic/primitives.py:1584: UserWarning: specified the name of the direction vector
  return DirectionalSourceDerivative(
/firedrake/src/sumpy/sumpy/kernel.py:1246: UserWarning: specified the name of the direction vector
  return type(kernel)(
/firedrake/src/firedrake/firedrake/external_operators/potential_evaluation/potentials.py:196: UserWarning: Functions in continuous function space will be projected to/from a 'Discontinuous Lagrange' space. Make sure any operators evaluated are continuous. Pass warn_if_cg=False to suppress this warning.
  warn("Functions in continuous function space will be projected "
/firedrake/src/loopy/loopy/target/execution.py:185: ParameterFinderWarning: Unable to generate code to automatically find 'nunit_dofs' from the shape of 'dst':
division with remainder in linear solve for 'nunit_dofs'
  warn("Unable to generate code to automatically "

Traceback (most recent call last):
  File "doublelayer_sphere.py", line 20, in <module>
    K = DoubleLayerPotential(u1, LaplaceKernel(dim=3), places, actx=actx, function_space=V, op_kwargs={'qbx_forced_limit': None})
  File "/firedrake/src/firedrake/firedrake/external_operators/abstract_external_operators.py", line 133, in evaluate
    return self._evaluate_action(x, *args, **kwargs)
  File "/firedrake/src/firedrake/firedrake/external_operators/potential_evaluation/potentials.py", line 144, in _evaluate_action
    return self._evaluate()
  File "/firedrake/src/firedrake/firedrake/external_operators/potential_evaluation/potentials.py", line 105, in _evaluate
    return self._eval_potential_operator(self.density, out=self)
  File "/firedrake/src/firedrake/firedrake/external_operators/potential_evaluation/potentials.py", line 99, in _eval_potential_operator
    return self.connection.to_firedrake(potential, out=out)
  File "/firedrake/src/firedrake/firedrake/external_operators/potential_evaluation/pytential.py", line 190, in to_firedrake
    self.target_to_meshmode_connection.from_meshmode(evaluated_potential)
  File "/firedrake/src/meshmode/meshmode/interop/firedrake/connection.py", line 515, in from_meshmode
    self._validate_field(mm_field, "mm_field", dtype=dtype)
  File "/firedrake/src/meshmode/meshmode/interop/firedrake/connection.py", line 356, in _validate_field
    check_dof_array(field, field_name)
  File "/firedrake/src/meshmode/meshmode/interop/firedrake/connection.py", line 349, in check_dof_array
    raise ValueError(f"'{arr_name}.entry_dtype' must be {dtype},"
ValueError: 'mm_field.entry_dtype' must be float64, not 'complex128'

cc @benSepanski