Elastic Vertical Transverse Isotropic (VTI) wave solver implementation

[acitrain]

In this PR, we add the Elastic VTI physic for the second order wave solver.

The main difference between this one and the isotropic case (ElasticWaveEquationSEM.cpp) is the elasticity tensor C which is different.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 93.96887% with 31 lines in your changes are missing coverage. Please review.

Project coverage is 53.45%. Comparing base (4696a65) to head (aa3aa30).

Files	Patch %	Lines
...vers/wavePropagation/ElasticVTIWaveEquationSEM.cpp	92.68%	30 Missing :warning:
...vers/wavePropagation/ElasticVTIWaveEquationSEM.hpp	87.50%	1 Missing :warning:

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3060      +/-   ##
===========================================
+ Coverage    53.20%   53.45%   +0.24%     
===========================================
  Files          989      994       +5     
  Lines        83456    83970     +514     
===========================================
+ Hits         44405    44886     +481     
- Misses       39051    39084      +33     

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