Updating Minetest to 5.9.0

[Jan Wielkiewicz <tona_kosmicznego_smiecia@interia.pl>]

Hi,

I plan upgrading Minetest to 5.9.0 but there are some technical issues
that need to be addressed first.
Minetest developers dropped development of "Minetest Game" (MTG) - the
default game that was previously shipped with the engine:
https://blog.minetest.net/2023/12/04/5.8.0-released/
There are other games for Minetest that are not MTG, e.g. MineClone2,
NodeCore, etc. And mods made for the other games don't always work with
MTG.
As far as I can tell minetest-build-system tests all mods only against
MTG.
Given that MTG is not a default/official game anymore I decoupled the
minetest package and added a new minetest-minetest-game package for
people who for watever weird reason want to download the game anyway.
The question is: what should I do about the build system?

I also deprecated the irrlicht-for-minetest package, because minetest
devs copied it directly into the game's directory tree and minetest is
incompatible with upstream irrlicht anyway
(https://github.com/minetest/minetest/commit/f638482fba9cf4148ced66e1598cb9027a60cdc9).
The irrlicht-for-minetest package is not used outside of minetest.

I also plan updating minetest mods in Guix because they're really out
of date.

--

Greetings
Jan Wielkiewicz