Do not hardcode path to BeamNG.Drive compatdata

[WhiteHusky]

This issue is serving mostly as a reminder and documentation to how it might be done properly

This is a potential problem for people who might've installed BeamNG.Drive on a different Steam library, thus changing where the Proton prefix is stored on Linux.

Some research finds that the locations of all the library folders are specified in:
~/.local/share/Steam/config/libraryfolders.vdf

The file does indicate if an AppID is installed there so the flow is:

• Enumerate each location in libraryfolders.vdf
• For each location, see if AppID 284160 (BeamNG.Drive) is located there
• Our corrected path will become $library/compatdata/284160/