[XR] Failproof the snippet reference in NearInteraction

[RaananW]

Near Interaction feature in XR references the following snippet from our snippet server - https://github.com/BabylonJS/Babylon.js/blob/master/packages/dev/core/src/XR/features/WebXRNearInteraction.ts#L845

We should allow overriding this with the same content. For that we should provide this snippet as a JSON file as part of the assets in the core library or the assets library.
Loading/initialization should never fail, even if the snippet server is offline.