With the CMake changes to IrrlichtMt, it's now possible to use a target for IrrlichtMt.
Besides greatly improving the ease of setting up IrrlichtMt for users building the client, it removes the need for Minetest's CMake to include transitive dependencies such as image libraries, cleaning it up a tiny bit. The PR works by finding the IrrlichtMt package and linking to the target it provides. If the package isn't found and it isn't building the client, it will still fall back to using just the headers of old Irrlicht or IrrlichtMt.
Formspec element to display models, written by @kilbith, rebased and tweaked.
Co-authored-by: Jean-Patrick Guerrero <jeanpatrick.guerrero@gmail.com>
Co-authored-by: sfan5 <sfan5@live.de>
Add override targets for all special_tiles entries in node definitions, allowing texture packs to replace these textures. This makes overrides work properly with a variety of drawtypes.
The targets are named special1 through special6, covering the the current length of the special_tiles array.
