Add Samsung Galaxy XR controller assets

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WIP change to add Galaxy XR controller assets. Controllers are fully rigged, but not merging just yet because:

• Controller colors do not match physical device (black instead of grey)
• Have not had an opportunity to validate that the controllers align properly with the physical devices

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Got the updated controller models from android/android-xr-unity-package#11 which match the shipped device. Still have not had a chance to verify that they line up correctly with the controllers in-device but I'm inclined to land for now and adjust as needed when I have the controllers in hand in a week or so. Any misalignment should be relatively minor in the meantime.