Add some sort of emission masking support to the Layered parallax Shader

[orels1]

Currently, each layer of the Layered Parallax shader can only glow as a single unit

It would be nice to be able to make only specific parts of the texture glow, instead of everything glowing together.

One idea could be - adding a texture slot where each channel can be used as an emission mask. and then adding an Enum to each layer that allows you to pick a channel from that mask and set an extra emission color as an option