Feature/area extraction test

[antons-it]

Area extraction unit tests that fails with -np > 2

[FussyDuck]

All committers have signed the CLA.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 83.63636% with 18 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.11%. Comparing base (5dc85c9) to head (c1dd11b).
⚠️ Report is 572 commits behind head on develop.

Files with missing lines	Patch %	Lines
...olation/test_interpolation_structured2D_to_area.cc	88.00%	9 Missing ⚠️
...as/meshgenerator/detail/StructuredMeshGenerator.cc	0.00%	4 Missing ⚠️
src/atlas/util/GridPointsJSONWriter.cc	83.33%	3 Missing ⚠️
src/atlas/grid/StructuredPartitionPolygon.cc	80.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #179      +/-   ##
===========================================
+ Coverage    80.07%   80.11%   +0.03%     
===========================================
  Files          859      860       +1     
  Lines        63682    63781      +99     
===========================================
+ Hits         50993    51095     +102     
+ Misses       12689    12686       -3     

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[wdeconinck]

This test is still failing with MPI_SIZE = 120 and with grid O400.
Partition 76 coincidentally ends up with only very few points for which a mesh cannot be generated.

A workaround, but NOT the solution, could be choosing different MPI_SIZE (e.g. 128) or moving the area domain to include more points on partition 76 (or none at all).

[wdeconinck]

This test is still failing with MPI_SIZE = 120 and with grid O400.

Other possibility is to use functionspace::PointCloud as a target. Then no mesh is attempted to be generated for partition 76