Add ".xrOS" in the Package.swift for supporting the visionOS system.

[SKbarbon]

Add ".xrOS" in the Package.swift for supporting the visionOS system. This package is being used in my application, and I am planing for supporting visionOS.

[Recouse]

Added visionOS in the 8c0af68, please check if it works for you, then I'll create a new release

[Recouse]

Added in 0.0.6