Pseudo-Acoustic TTI Solvers

[Bertbk]

This PR follows another one on the VTI solvers https://github.com/GEOS-DEV/GEOS/pull/2816

• 2 new acoustic TTI solvers AcousticTTIFletcher AcousticTTIZhang
• Computation of the rotated Stiffness matrices
• Solver documentation (.rst)
• input files for each solvers
• unit test files for each solvers

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 37.95344% with 1146 lines in your changes are missing coverage. Please review.

Project coverage is 53.09%. Comparing base (d3783ad) to head (992e669).

:exclamation: Current head 992e669 differs from pull request most recent head 9c8c5ee

Please upload reports for the commit 9c8c5ee to get more accurate results.

Files	Patch %	Lines
...Propagation/AcousticTTIFletcherWaveEquationSEM.cpp	9.16%	317 Missing :warning:
...avePropagation/AcousticTTIZhangWaveEquationSEM.cpp	8.95%	315 Missing :warning:
...ation/AcousticTTIFletcherWaveEquationSEMKernel.hpp	0.00%	155 Missing :warning:
...pagation/AcousticTTIZhangWaveEquationSEMKernel.hpp	0.00%	150 Missing :warning:
...Propagation/AcousticVTIFletcherWaveEquationSEM.cpp	80.69%	67 Missing :warning:
...rmulations/Qk_Hexahedron_Lagrange_GaussLobatto.hpp	0.00%	45 Missing :warning:
...ation/AcousticVTIFletcherWaveEquationSEMKernel.hpp	78.26%	30 Missing :warning:
...pagation/AcousticVTIZhangWaveEquationSEMKernel.hpp	63.46%	19 Missing :warning:
...ropagationTests/testWavePropagationTTIFletcher.cpp	38.70%	19 Missing :warning:
...vePropagationTests/testWavePropagationTTIZhang.cpp	38.70%	19 Missing :warning:
... and 4 more

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3008      +/-   ##
===========================================
- Coverage    53.57%   53.09%   -0.48%     
===========================================
  Files         1003      991      -12     
  Lines        85297    84380     -917     
===========================================
- Hits         45695    44800     -895     
+ Misses       39602    39580      -22     

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