Update UnityFileSystemApi to 6000.3.0b6

Replace earlier drop (from 6000.2.6f1) with version as shipped in 6000.3.0b6.

* Windows was extracted by installed in UnitySetup64-6000.3.0b6.exe and copying file from C:\Program Files\Unity\Hub\Editor\6000.3.0b6\Editor\Data\Tools
* Linux was extracted from Unity-6000.3.0b6.tar.xz from Unity-6000.3.0b6.tar\Editor\Data\Tools\ (Using 7z)
* OSX was extracted from Unity-6000.3.0b6.pkg from Unity.pkg.tmp\Payload\Payload~\.\Unity\Unity.app\Contents\Frameworks\  Note: ion 6.2 it had been shipped in Unity.app\Contents\Tools\

Author: SkowronskiAndrew