Bug(?): ATI1N VTFs appear red when used for basetextures

[lenship2]

Describe the bug

ATI1N is a VTF format for greyscale textures that only has a single channel. Right now it's ideal for stuff like texture masks that you would want as a separate texture referenced by the vmt. However, it's current drawback is that it can't be used effectively for greyscale basetextures: the engine reads ATI1N textures as only a red channel for basetextures, meaning that if you use one for a basetexture, it'll appear red in game. This limits the usage of the format, making it only useful for stuff like the aforementioned texture masks.

I'm aware that I8 doesn't have this issue, but I think that ATI1N shouldn't either, given that it's overall a better format with gpu compression.

To Reproduce

1. Apply provided material to a surface and observe how it's red instead of grey

Issue Map

some test materials
a.zip

Expected Behavior

ATI1N textures used for the basetexture should appear entirely greyscale in the engine, rather than it only displaying as a red channel.

Operating System

No response

[craftablescience]

This requires a change in shader code to copy the value to all channels (similar issue with BC5/ATI2N but cheaper)