Update UFL element interface

[mscroggs]

These changes (and firedrakeproject/tsfc#300 and NGSolve/ngsPETSc#5) will be required once FEniCS/ufl#197 is merged into the Firedrake fork of UFL

Docs build on CI is failing as it's using the wrong UFL branch.

[ksagiyam]

Hi Matt,

Thanks for working on this. It turned out that this was my fault.
This failing piece shouldn't be tested in parallel, as variable layer extrusion is broken in parallel: #2169.
Could you please make tests/output/test_io_mesh.py::test_io_mesh_uniform_variable_layers a serial test (just by removing the @pytest.mark.parallel(nprocs=3))?

I do not know why this test has been passing, and why your changes exhibit the issue, but this test is not expected to work in parallel.

I'm sorry.

[mscroggs]

Hi Matt,

Thanks for working on this. It turned out that this was my fault. This failing piece shouldn't be tested in parallel, as variable layer extrusion is broken in parallel: #2169. Could you please make tests/output/test_io_mesh.py::test_io_mesh_uniform_variable_layers a serial test (just by removing the @pytest.mark.parallel(nprocs=3))?

I do not know why this test has been passing, and why your changes exhibit the issue, but this test is not expected to work in parallel.

I'm sorry.

No need to be sorry, this is great news, as it means I haven't broken anything major!

[mscroggs]

Closing this in favour of #3166