com.unity.xr.arkit 4.0.8 Package Notes

Fixed an issue where ARKit shaders could incorrectly remain in the Preloaded Assets array, which could interfere with builds on other platforms. For example, in some cases, if first you built for iOS, and then built for Android, you might have seen an error message like
```
Shader error in 'Unlit/ARKitBackground': failed to open source file: 'Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl' at line 44 (on gles3)
```
Fixed crash on startup caused by devices that support iOS 11 but not ARKit.
Fixed memory leak in the meshing subsystem implementation from unreleased MTLBuffers.

com.unity.xr.arkit 4.0.8