Godot Image::normal_map_to_xy Unclear Description

**Your Godot version:**
Godot 4.3

**Issue description:**
The description for the `Image` class's `normal_map_to_xy` adds absolutely no clarity as to what it does:

> Converts the image's data to represent coordinates on a 3D plane. This is used when the image represents a normal map. A normal map can add lots of detail to a 3D surface without increasing the polygon count.

Having read this description, I still have literally no clue what this does. Seems like it could be useful, but it describes no use cases; only that it's somehow related to normal maps. It appears the only way to find out what it actually does would be to test it, meaning the documentation has not done its job.

**URL to the documentation page (if already existing):**
https://docs.godotengine.org/en/stable/classes/class_image.html#class-image-method-normal-map-to-xy