Symlink _GM name, fixes T8427
This adds a symlink to the FluidR3_GM.sf2. Our was just called FluidR3.sf2 because the other file (FluidR3_GS.sf2) wasn't working anymore, so to make it more understandable for users, we dropped _GM. Apparently some (not many) programs actually check for _GM explicitly without letting the user choose it manually.
Test Plan: - Verify that the file is installed correctly.
Reviewers: Triage Team, JoshStrobl
Reviewed By: Triage Team, JoshStrobl
Maniphest Tasks: T8427
Differential Revision: https://dev.getsol.us/D7482