API for light intensity and color at night and day

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Add compact, short information about your PR for easier understanding:

• Allows games to change sun color, intensity, and night's darkness.
• It changed get_sunlight_color function, so no constants are used for sun color calculation, but configurable parameters.
• This can be useful with mods that control moon phases and weather. It also can be useful in space games.
• With this, heavy cloudy nights can be darkness than normal nights, etc.

To do

This PR is Ready for Review.

How to test

Run game devtest and run command set_light_intensity from lighting mod.

Screen.Recording.2024-01-02.at.17.47.51_480.mov

[Zughy]

only went through the DOCS. It'd be also nice having some pictures or a small video

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@appgurueu @Zughy Fixes, feedback applied, rebased, and a small video added (to PR itself).

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Rebased, merged to one commit, and cleaned Lua code

[Andrey2470T]

I've made some testing of this feature. I assume it actually should depend now on #14789 as it repairs generally applying any colorful light values to the common vertex light color and this PR is not an exception also.

At the set single-channel color offsets the devtest player model gets fully dark. It happens on adjusting the red and blue channels:

The particles are not affected by the sunlight color at all with any combinations of the offsets and coefficients:

The color of the nodes going with such paramtype2 as colorfacedir (and I'm sure also other its colorized analogues) randomly diverges with the actual set sunlight color. This much possibly happens of that issue (wrong mixing of the different light colors together with the hardware one):

[Andrey2470T]

I think it is worth to change the check for the bytes availability in the packet doing it similar with https://github.com/minetest/minetest/pull/14343/files#diff-592338f1bfb0275512da218625ce67e993b91984c175f70fe376825ab4e0aad2R1804

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This is the normally used style.
I will change it in the rebase after PR #14343 is merged.

[nerzhul]

why localplayer is included here ? we should not have player inclusion on mapblock_mesh, which is close to render and has nothing to do with player session/object

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Because the light setting is stored in the local player.

[Andrey2470T]

If the shaders are disabled, the new sunlight color on the mapblocks meshes should be appeared immediately after updating it in LocalPlayer. You could keep some flag signalizing about that somewhere in the ClientMap and then call MapblockMesh->animate() on all visible mapblock meshes. Because currently this circumstance leads to the following artifacts:

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At the set single-channel color offsets the devtest player model gets fully dark. It happens on adjusting the red and blue channels:

The particles are not affected by the sunlight color at all with any combinations of the offsets and coefficients:

The color of the nodes going with such paramtype2 as colorfacedir (and I'm sure also other its colorized analogues) randomly diverges with the actual set sunlight color. This much possibly happens of that issue (wrong mixing of the different light colors together with the hardware one):

No affected particles are a bug. I will check it.

When texture without red color is shown as black in the light which does not include the red part, it is not a bug.
You cannot expect that a surface that can reflect only red light, will reflect green or blue light.

This PR should affect only the color of sunlight, not the color of light from artificial light sources.
You cannot expect that the pure red texture will reflect pure green light.

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Rebased, sky color is applied also to particles.

[Zughy]

@sfence rebase needed