Fastscape c++ coupling [WIP]

[Minerallo]

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The existing coupling between ASPECT and FastScape, developed by Derek Neuharth and Anne Glerum, utilizes the Fortran version of FastScape. However, this Fortran version is no longer being actively developed. I want to couple ASPECT with the actively developed C++ version of FastScape (Fastscapelib), which will incorporate an unstructured grid and be parallelized. This will make ASPECT - FastScape working with large scale spherical models. I have integrated the Fastscape C++ library to the contrib folder and added the paths to the Cmakelist. I re-use some of the fastscape fortran interface from PR #4396 to develop the initial FastScapecc (.cc, .h) which call the Stream Power law erosion function of fastscapelib.

I added a test case repository in tests repository with a output_screen but it is not working yet. It runs for few timesteps and crashes sending malloc errors.

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