Load entity meshes from gltf/glb files (#2762)

Requires #2733 and #2680 

Progress towards #2419 and #87

progress towards #2777
fixes #2830

So far only works in blockbench coordinate system (right handed, y-up,
z-forward) converting it to our system, so for now you have to be sure
you export your mesh in the right system if its from another program.
Doesn't load textures so they are still stored in game assets. This is a
really simple start that i will build up on in future PRs.

A few questions still remain:
- ~~Do we want to keep the legacy .obj loading?~~ (no, because in a
later pr when i add joints i wont be able to add them and it will brake
stuff, and thats generally useless)
- ~~Do we want to load the file data ourselves and then feed it into the
cgltf or just let cgltf handle that~~ (turns out there is no problem
with that so its best to do that so that we can have local allocations)
- Do we want to override cgltf allocation functions?
- ~~Do we want to try handle other possible edge cases that might happen
when exporting from other applications? (like different coordinate
systems and stuff)~~ (yes #2777)

---------

Co-authored-by: till++ <tillplusplus@gmail.com>
Co-authored-by: careeoki <122191047+careeoki@users.noreply.github.com>
Co-authored-by: tillpp <tillpp@users.noreply.github.com>
Co-authored-by: IntegratedQuantum <43880493+IntegratedQuantum@users.noreply.github.com>

Author: 4 people

assets/cubyz/entityModels/cubert.zig.zon

@@ -2,4 +2,5 @@
 	.model = "cubyz:cubert",
 	.defaultTexture = "cubyz:cubert",
 	.height = 2,
+	.coordinateSystem = .right_handed_z_up,
 }

assets/cubyz/entityModels/missing.zig.zon

@@ -2,4 +2,5 @@
 	.model = "cubyz:missing",
 	.defaultTexture = "cubyz:missing",
 	.height = 1,
+	.coordinateSystem = .right_handed_y_up,
 }