Add missing update_trian! method for MultiField

[zjwegert]

Handle MultiFieldFEFunction inputs for shape differentiation through differentiable triangulations. E.g., for the case φuh ∈ V_φu = MultiFieldFESpace([V_φ,U]),

dΩ = DifferentiableTriangulation(...,V_φ)
J_bulk_mult((φ,u)) = ∫(...)dΩ
gradient(J_bulk_mult,φuh)

the existing update_trian! implementation would do nothing because V_φu !== V_φ. The added method for multifield spaces checks each space to see if any are the space related to the DifferentiableTriangulation.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.04%. Comparing base (b492a2a) to head (96f4d97).
Report is 165 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #112      +/-   ##
==========================================
+ Coverage   73.99%   77.04%   +3.04%     
==========================================
  Files          18       31      +13     
  Lines        2546     3603    +1057     
==========================================
+ Hits         1884     2776     +892     
- Misses        662      827     +165     

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[JordiManyer]

@zjwegert Looks good. Update NEWS and I'll merge.

[zjwegert]

@JordiManyer FYI, I've also fixed precompilation in this PR. Waiting on tests.