updates EMC model routines (1d depth average/interpolation/tapering); initial work to support full gravity

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 15.22782% with 707 lines in your changes are missing coverage. Please review.

Project coverage is 40.55%. Comparing base (b6fa4b6) to head (3850570).

Files	Patch %	Lines
src/meshfem3D/SIEM_meshing.f90	0.00%	304 Missing :warning:
src/meshfem3D/test_MPI_interfaces.f90	1.92%	102 Missing :warning:
src/meshfem3D/setup_MPI_interfaces.f90	8.69%	84 Missing :warning:
src/meshfem3D/create_MPI_interfaces.f90	25.88%	63 Missing :warning:
src/meshfem3D/setup_inner_outer.f90	2.17%	45 Missing :warning:
src/meshfem3D/setup_color_perm.f90	3.70%	26 Missing :warning:
...ocess_sensitivity_kernels/create_cross_section.F90	0.00%	25 Missing :warning:
src/shared/read_compute_parameters.f90	22.58%	24 Missing :warning:
src/meshfem3D/create_regions_mesh.F90	50.00%	7 Missing :warning:
src/meshfem3D/save_arrays_solver.f90	73.68%	5 Missing :warning:
... and 11 more

Additional details and impacted files

```diff @@ Coverage Diff @@ ## devel #831 +/- ## ========================================== - Coverage 40.96% 40.55% -0.42% ========================================== Files 263 264 +1 Lines 57835 58572 +737 ========================================== + Hits 23694 23754 +60 - Misses 34141 34818 +677 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[danielpeter]

will merge for now - Mac testing needs fixing later on...