Pullbacks

[JordiManyer]

Notes for future self:

• I am using the pre-existing machinery of LinearCombinationMap to do the basis changes. This includes modifying LinearCombinationDofVector to use it. I have then had to modify ReferenceFEs.compute_dofs to use the transpose of the change (due to how linear combinations deals with indices).
• Since most changes will be sparse/diagonal, we should create some dispatching that takes advantage of it when evaluating LinearCombinationMap (TODO)
• Right now the changes are the same in both directions. However, we will require an inverse+transpose map applied to the matrix of the change. I think this can be done in one go, but how to make it elegant?

Now that we have the skeleton for these features, I will merge and continue implementing this in the moment-based-reffes branch.

[codecov]

Codecov Report

Attention: Patch coverage is 31.93117% with 1424 lines in your changes missing coverage. Please review.

Project coverage is 83.89%. Comparing base (3b87738) to head (ba8261a).
Report is 79 commits behind head on moment-based-reffes.

Files with missing lines	Patch %	Lines
src/Polynomials/ChebyshevPolynomialBases.jl	0.00%	341 Missing ⚠️
src/ReferenceFEs/deprecated/RaviartThomasRefFEs.jl	0.00%	266 Missing ⚠️
src/ReferenceFEs/deprecated/NedelecRefFEs.jl	0.00%	197 Missing ⚠️
src/Polynomials/PCurlGradJacobiPolynomialBases.jl	0.00%	179 Missing ⚠️
src/FESpaces/deprecated/DivConformingFESpaces.jl	0.00%	94 Missing ⚠️
src/ReferenceFEs/deprecated/BDMRefFEs.jl	0.00%	88 Missing ⚠️
src/ReferenceFEs/MomentBasedReferenceFEs.jl	76.85%	56 Missing ⚠️
src/ReferenceFEs/AWRefFEs.jl	0.00%	38 Missing ⚠️
src/ReferenceFEs/MTWRefFEs.jl	0.00%	30 Missing ⚠️
src/ReferenceFEs/HHJRefFEs.jl	0.00%	29 Missing ⚠️
... and 14 more

Additional details and impacted files

@@                   Coverage Diff                   @@
##           moment-based-reffes    #1067      +/-   ##
=======================================================
- Coverage                89.04%   83.89%   -5.16%     
=======================================================
  Files                      197      209      +12     
  Lines                    23887    25348    +1461     
=======================================================
- Hits                     21270    21265       -5     
- Misses                    2617     4083    +1466     

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