Interpolate multifield

[oriolcg]

No description provided.

[codecov-commenter]

Codecov Report

Merging #279 into master will increase coverage by 0.02%.
The diff coverage is 94.80%.

@@            Coverage Diff             @@
##           master     #279      +/-   ##
==========================================
+ Coverage   88.26%   88.28%   +0.02%     
==========================================
  Files         153      153              
  Lines        9963    10023      +60     
==========================================
+ Hits         8794     8849      +55     
- Misses       1169     1174       +5     

Impacted Files	Coverage Δ
src/FESpaces/FESpaces.jl	100.00% <ø> (ø)
src/MultiField/MultiField.jl	100.00% <ø> (ø)
src/FESpaces/CLagrangianFESpaces.jl	96.29% <50.00%> (ø)
src/FESpaces/ZeroMeanFESpaces.jl	79.59% <66.66%> (-3.02%)	⬇️
src/FESpaces/SingleFieldFESpaces.jl	85.90% <93.93%> (+0.42%)	⬆️
src/FESpaces/DirichletFESpaces.jl	75.00% <100.00%> (ø)
src/FESpaces/ExtendedFESpaces.jl	94.73% <100.00%> (ø)
src/FESpaces/FESpacesWithLastDofRemoved.jl	87.71% <100.00%> (+1.44%)	⬆️
src/FESpaces/FESpacesWithLinearConstraints.jl	95.02% <100.00%> (+0.06%)	⬆️
src/FESpaces/TrialFESpaces.jl	93.33% <100.00%> (-1.91%)	⬇️
... and 3 more

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[fverdugo]

@oriolcg Nice work!

I have added some minor comments.

Can you also add few lines in NEWS.md about the changes/additions?

In the "Added" section, say something like interpolation is now supported also for multifield spaces. In the "Changed" section, say something in the direction that the SingleFieldFESpace interface has changed. A new function gather_free_and_dirichlet_values! is added as mandatory and the old one gather_free_and_dirichlet_values is now optional.

Thanks!

[oriolcg]

Requested modifications added in the recent commit.