Godot texture masking (mask channels)

### Tested versions

4.3

### System information

Godot v4.3.stable (77dcf97d8) - Freedesktop SDK 23.08 (Flatpak runtime) - X11 - Vulkan (Forward+) - dedicated NVIDIA GeForce RTX 2060 SUPER (nvidia) - Intel(R) Core(TM) i5-9400F CPU @ 2.90GHz (6 Threads)

### Issue description

GLTF model can have one material (surface) and multiple texture on this. It displays as some pseudosurfaces what are green, red, blue or black.
So question: how i can set all these textures? i tried use all texture variants and not found variant for me.

### Steps to reproduce

Have this strange model (change first .txt to .gltf and next .txt to .bin)
l[SM_NeighborsHouse_part15.txt](https://github.com/user-attachments/files/18049270/SM_NeighborsHouse_part15.txt)
[SM_NeighborsHouse_part15.txt](https://github.com/user-attachments/files/18049275/SM_NeighborsHouse_part15.txt)

### Minimal reproduction project (MRP)

Create empty project and then add this model and try add some textures or materials

Start by importing the attached GLTF/BIN files into the empty Godot project and reproducing the material with its multiple textures. Inspect how the single material and texture channels are represented; the issue is ready when the channel-masking behavior is understood well enough to document the correct setup or define a reproducible engine defect.

Written by the indexing model from the issue text.