Inner and outer textures for end gateway beam cannot be textured independently

The bug

Both the opaque inner and translucent outer sections of the end gateway beam will use the same texture file, making it impossible to give them separate textures.

How to fix

Make end gateway beams use two texture files - one for the inner beam, and another for the outer beam.

Ideally, both should support translucent pixels as to fix MC-164001, and the outer beam's translucency should not be hardcoded but instead depend on the alpha values of the texture file.