Add Perlin and Simplex noise

[kno10]

Add Perlin and Simplex noise using the FastNoiseLite library (did not try alternatives such as FastNoise2).

Incorporates #15858
Closes #11468

To test, set flags = perlin, compat or flags = simplex, compat (absvalue is also supported).

For compat, I tried to get scaling somewhat consistent with the vaule noise currently used, but it's not perfect.
First of all, the library limits the noise to -1:+1, whereas the Luanti code did not include any such rescaling. Secondly, Simplex noise is "by design" more dense than Perlin or value noise. So if you use existing scale parameters, it is suggested to use compat. But for a new use case (e.g., a new mapgen), I would suggest not using this.

You can have terrain as weird as before when the mountain generator is active:

but the axis-aligned artifacts of value noise are gone. For mountains, this makes them look too blob-like IMHO. Works well with valleys generator, too.

With the current value noise, because it interpolates between points sampled on a grid, such artifacts arise frequently (most visible in mountains, as these use fewer octaves -- the grid is very visible on the minimap, too):

[wmikita]

IMO it's weird for Perlin and Simplex noise implementations to be accessible by passing flags to a value noise implementation (especially considering they're clearly conflicting), even though "simplex" was already there as a not-yet-implemented somebody-was-assigned-this-11-years-ago-and-here-we-are flag.
from what I can see, this results in a cluttered value noise implementation, with the clutter having to weirdly adjust itself in order to be more like the value noise already present. I would suggest separate classed for both if not for backwards compatibility issues that would arise with PerlinNoise; how about a new GradientNoise class, and then make the specific noise used a string enum passed to the constructor?
also, I'm not sure why anybody would want to use the compat flag? what compatibility does it actually provide?

[kno10]

Well, I did not want to break any compatibility by introducing a new API.
The compat mode allows you to easily use the current mapgen defaults, but with a smoother noise.
In particular for exploring the difference it is nice if you can use the noise with existing mapgens.
At the same time, it does not break any existing world.

New mapgens may use Perlin or Simplex noise by default, with new default scales that work well with standard parameters. Note that Simplex noise is about 15% finer than Perlin noise by design, so ultimately mapgen developers will likely focus on one of them (most likely Simplex, although it is a bit slower than Perlin noise unless this higher density allows us to reduce the number of octaves).

As for clutter, some of the code duplication is intentional to make it easier for the compiler to inline, e.g., have the conditionals rather outside of hot loops and duplicate the loop code.

[sfence]

Break compatibility is caused by renaming PerlinNoise in LUA mod API for example.

[sfence]

@kno10 Sorry, my error I miss line lua_register(L, "PerlinNoise", create_object); // deprecated name.