Remove remaining deprecations

[masterleinad]

Rebased on top of #15611.
Deprecated in:

• Remove remaining create_triangulation_compatibility calls. #12049
• Rename PETScWrappers::PreconditionerBase to PreconditionBase #11670
• Remove the base-case overload of cell_measure. #12219
• Add new MappingQCache::initialize() function #11867
• Move LinearAlgebra::CommunicationBase -> Utilities::MPI::CommunicationBase. #11751
• Deprecate TriaAccessor::number_of_children. #12067

[marcfehling]

I like that you cleaned up the vertex ordering tests, especially as in getting rid of create_triangulation_compatibility(). Looked very tedious.

You duplicated some code to ensure mesh compatibility among some tests. I would suggest to move these functions into a separate header file, or extend the existing one tests/test_grids.h which right now only has mesh generators, but it would be predestined for the vertex reordering. Then we have everything in one spot.

[masterleinad]

@marcfehling See 0096280 (#15629).

[marcfehling]

@marcfehling See 0096280 (#15629).

I like it!

Technically we could also use these functions on tests/bits/neighboring_cells_at_two_faces.cc, tests/data/data_out_curved_cells.cc, tests/grid/grid_invert_02.cc, and tests/grid/line_coarsening_3d.cc to preserve the original state of the test. Probably not necessary, I don't feel strong about it. How do you think about it?

[masterleinad]

Technically we could also use these functions on tests/bits/neighboring_cells_at_two_faces.cc, tests/data/data_out_curved_cells.cc, tests/grid/grid_invert_02.cc, and tests/grid/line_coarsening_3d.cc to preserve the original state of the test. Probably not necessary, I don't feel strong about it. How do you think about it?

I would rather convert all the tests instead of using the new function but that seemed to be too much work.