PBR refractions are incorrect when useRightHandedSystem = true

PBRMaterial (and NodeMaterial) refractions are incorrect if scene is using right handed coordinate system.

Playground example: Babylon.js Playground

See how the background doesn’t line up with the rendered refraction even with near 1.0 IOR. Left handed coordinate system works correctly.

Here is a test case for NodeMaterial: Babylon.js Playground

Looks like that one only happens when environment texture matrix has been rotated.

cc @Evgeni_Popov

This PR will fix the problem: