[no sq] Increase strictness for item registration / overrides

[sfan5]

see #15091
also: the discussion in #15910 and on IRC

Note: this breaks Voxelibre, because they try to register aliases a few seconds after the game starts.

To do

This PR is Ready for Review.

[SmallJoker]

I enabled a few of the commonly used mods for MTG. No breakages found.

$ grep "load_mod_" world.mt | grep "= mods/" | wc -l
157

Mineclonia works.
Repixture works.
VoxelLibre works

[kno10]

It does appear that this can crash VL due to the HELP/mcl_item_id mod, when some structure spawns with an enchanted item. I'm not sure what that mod is actually good for, it seems to hook into the tooltip system for addons to add some debugging tooltips and could simply be dropped. Mineclonia appears to have deleted that mod a year ago already.