build/solids: fix order/uninitialized variable

solids - add libCEED coarse level assembly

examples/petsc/multigrid: assemble matrix analytically instead of coloring

This currently requires development PETSc to correctly handle negative
indices through the LocalToGlobalMapping.

petsc - set minimum version for examples

doc(fluids): Correct vector name in Tau dropdown

Otherwise $$\hat{\bm{n}}$$ is never defined.

style - make qf/op field names human readable

petsc - use DMPlexGetLocalOffsets for building restrictions

examples/fluid: set c_tau = 0.5

eulervortex: add test_5 - non-smooth cylinder

Scale velocity to user defined units in traveling vortex and advection(2d)

examples/fluids: explain edge measures and wave speeds

doc: explain tau for conservative variables

Update doc/sphinx/source/references.bib

examples/fluids: tau as spatial criterion 2 of hughesetal2010

Testing traveling vortex with

$ build/fluids-navierstokes -problem euler_vortex -ts_adapt_monitor -lx 1000 -ly 1000 -lz 50 -dm_plex_box

examples/fluids: tau as spatial criterion 2 of hughesetal2010

Testing traveling vortex with

$ build/fluids-navierstokes -problem euler_vortex -ts_adapt_monitor -lx 1000 -ly 1000 -lz 50 -dm_plex_box_faces 20,20,1 -ts_adapt_safety 0.8 -implicit -snes_atol 1e-3 -ksp_atol 1e-4 -ksp_rtol 1e-3 -ts_type alpha -ts_dt 0.1 -ksp_type bcgs -pc_type lu -log_view -snes_monitor -ksp_monitor -snes_converged_reason -output_freq 1 -degree 1 -ts_max_time 5. -stab supg -snes_lag_jacobian 30 -snes_lag_jacobian_persists -snes_mf_operator

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examples/fluids docs: explain stabilization

fluids - fix flux Jacobian and add su/supg to euler_vortex

rust - use for-in over for_each when not using iterator chain

rust - fix ex3 and ex4 for new vector access protections

vec/qf - initial valid/borrowed/owned split for data (#853)

* vec/qf - initial valid/borrowed/owned split for data

* vec/qf - tidy logic for checking active/stale data

* minor - add missing NU

vec/qf - initial valid/borrowed/owned split for data (#853)

* vec/qf - initial valid/borrowed/owned split for data

* vec/qf - tidy logic for checking active/stale data

* minor - add missing NULL

* doc - explain VectorTakeArray update

* minor - update error messages

* test - update error message in junit/tap

* gpu - fix stray CeedScalar vs void for QFunctionContext

* vec/qf - clarify/simplify access logic

* vec - calloc host arrays when no value set to make empty

* style - minor

* style - minor

* minor - fix error messages

* vec/qf - move data validity checking to backend interface

* gpu - add missing sync error checking for qfcontext

* gpu - homogonize use of impl for backend data to reduce confusion

* vec - clarify access conditions

* python - update test for stricter vector access

* vec - minor fixes

* minor - fix ipython change

* vec - add missing declarations in ceed/backend.h

* ctx - mirror vector borrowed data check in ctx interface

* vec - add CeedVectorGetArrayWrite

* vec - consistent use of CeedVectorGetArray vs CeedVectorGetArrayWrite

* python - small vec fixes

* doc - describe vector data semantics

* magma - update restriction

* gpu - fix restr bug I added, need to sum into target

* magma - fix restriction bug

* cpu - fix restriction bug here too

* op - fix evec allocations

* julia - fix ElemRestriction for new vector access rules

* op - double check GetArray vs Read vs Write usage

* doc - small fix

* restr - clean up read/write logic for restr

* python - add vec.array_write

* magma - typo fix

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rust - scale each component seprately for ex3 and ex4

rust - add ex3 and ex4 for vector problems

petsc - use PetscFECreateLagrange

Solids: fixed duplicate definitions in structs.h

qf - drop unneeded guards on math.h

Merge pull request #812 from CEED/jeremy/check-op

Promote Operator check to public API; Strengthen composite Operator check