Use autodiff in find_local_coordinate

[KnutAM]

PR towards #820

A way to avoid introducing calculate_mapping_and_spatial_coordinate, but without MixedTensors, it is not as nice as it could be

[KnutAM]

As pointed out by @termi-official on slack and by CI failure - requires MixedTensors for the autodiff to work as intended for embedded elements....

[KnutAM]

Added ForwardDiff as dep to make it work.

Timings show faster for regular but slower for embedded. Probably since the workaround requires double evaluation of shape functions.

@btime PointEvalHandler($mesh, $points); 
# Standard elements from test_pe_scalar_field in test_pointevaluation.jl
PR876:  78.600 μs (423 allocations: 59.38 KiB)
PR820:  89.000 μs (423 allocations: 59.38 KiB)
# Embedded elements from test_pe_embedded in test_pointevaluation.jl
PR876: 903.100 μs (4319 allocations: 988.27 KiB)
PR820: 857.400 μs (4319 allocations: 988.27 KiB)

Edit: Closing this again but have it as a reference for the discussion in #820, I think it would be nice to reuse the spatial_coordinate function introduced there with the local coordinate \xi as input for defining the residual equation to solve for.

[codecov-commenter]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (dde8aac) 93.05% compared to head (0a6ff00) 92.86%.
Report is 2 commits behind head on do/fix-pointeval-geovalues.

Files	Patch %	Lines
src/FEValues/common_values.jl	66.66%	1 Missing ⚠️

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Additional details and impacted files

@@                      Coverage Diff                       @@
##           do/fix-pointeval-geovalues     #876      +/-   ##
==============================================================
- Coverage                       93.05%   92.86%   -0.20%     
==============================================================
  Files                              36       36              
  Lines                            5288     5300      +12     
==============================================================
+ Hits                             4921     4922       +1     
- Misses                            367      378      +11     

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