chore: respect the new folder structure inside of Unity

[bitsandfoxes]

The layout inside of the Unity installation changed and we need to update the path resolution for the dependencies the SDK has at build time. Since mucking around inside the .targets is a pain I extracted this into a single script that gets invoked by MSBuild.

Added the new paths to the .targets.
Old layout (Unity ≤ 6000.1.x, macOS):

  /Applications/Unity/Hub/Editor/<version>/Unity.app/
  └── Contents/
      ├── MacOS/
      │   └── Unity
      ├── Managed/
      │   ├── UnityEngine.dll
      │   ├── UnityEditor.dll
      │   └── UnityEngine/
      │       └── UnityEngine.*.dll (modules)
      └── Resources/
          └── PackageManager/...

New layout (Unity 6000.3.x, macOS):

  /Applications/Unity/Hub/Editor/<version>/Unity.app/
  └── Contents/
      ├── MacOS/
      │   └── Unity
      └── Resources/
          ├── PackageManager/...
          └── Scripting/
              └── Managed/
                  ├── UnityEngine.dll
                  ├── UnityEditor.dll
                  └── UnityEngine/
                      └── UnityEngine.*.dll (modules)

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