CMake symlink test data files

[alexbeattie42]

The CMake test data file copy has never worked properly for me and I usually need to manually copy files around.

Brief summary of changes

Symlink the test data files to the target directory. This has the advantage of avoiding excessive copying and preserving changes made to the source files. As of CMake 3.13 (released in 2018) -E create_symlink is supported on all platforms and OpenSim uses version 3.15.

Testing I've completed

• Ran locally
• CI success indicates the files are linked properly

Looking for feedback on...

CHANGELOG.md (choose one)

• no need to update because it is an internal change to configure CMake tests

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This change is 

[alexbeattie42]

@aymanhab @nickbianco could you take a look?

[aymanhab]

@alexbeattie42 If this actually works on windows that would be awesome and would solve a long standing issue with tests duplicating files. I Assume ci passing means it works on windows. If you have a local windows system to verify then please merge, otherwise let me know and I'll try to test it out before merging. Thank you 👍

[alexbeattie42]

@alexbeattie42 If this actually works on windows that would be awesome and would solve a long standing issue with tests duplicating files. I Assume ci passing means it works on windows. If you have a local windows system to verify then please merge, otherwise let me know and I'll try to test it out before merging. Thank you 👍

Thanks! Unfortunately I don't have a Windows system setup for development at the moment as I mostly work in Linux. I have used this same technique in other projects that were cross platform (Windows, Mac x86, Mac ARM) and it worked well there. I did briefly peruse the logs to ensure that the tests actually did run and didn't somehow silently fail because of lack of files and it appears that they all ran properly. Here is the link to the docs where it's noted that it works in Windows as of 3.13 which I forgot to link above. I can try to get things up and running in Windows but I think it may take a bit more time than I'm expecting.