Add Use Color and Use HDR properties to LightmapGI

[Calinou]

Follow-up to #50572.

Colored lightmaps and HDR lightmaps can be disabled to reduce file size, which is useful for mobile/web platforms.

This closes #50569 and closes #50570.

File size comparison in a given 3D scene:

• HDR enabled, color enabled (default): 9.80 MB
• HDR enabled, color disabled: 3.32 MB (3× smaller)
• HDR disabled, color enabled: 902 KB (11× smaller)
• HDR disabled, color disabled: 471 KB (21× smaller)

[reduz]

I think this is a misunderstanding of how lightmaps work in Godot 4.0, but may be good to improve the usability on this.

[Calinou]

I think this is a misunderstanding of how lightmaps work in Godot 4.0, but may be good to improve the usability on this.

What do you mean by misunderstanding? Changing an image's pixel format will reduce its size on disk. I don't think there's anything more involved 🙂

[Calinou]

Rebased and tested again, it works as expected. The file size differentials are even greater now, since we can use lossless WebP for LDR lightmaps instead of PNG 🙂

[Calinou]

Rebased and tested again, it works as expected. Note that this will benefit from #93440 when using large lightmaps and Use HDR disabled, as to sidestep the WebP format limitation of 16383×16383 pixels. This will be especially relevant after #94243.

[BlueCube3310]

Some things to consider:
Directional lightmaps will not work with non-hdr formats since the SH coefficients require a storage format that supports negative values,
Grayscale HDR will only affect the size of the exr image, not the imported one,
Non-hdr lightmaps work best for indirect (dynamic) lighting, direct (static) will usually exceed the maximal value.