Determine mod to blame from stacktrace

[Lars Müller]

Problem

#12236 plus Minetest having to store origins for every callback, setting them to a global register each time the callbacks run (ugh); this also fails if modders call callbacks (or insert them into the callback lists) manually.

Solutions

Minetest already generates a stacktrace localizing the functions. It may infer the responsible mod from the top of the stack trace.

Alternatives

Keep it the current, unreliable, inefficient way.

[sfan5]

Just like there are cases where the last running mod is not responsible there will be cases where the last mod in the stacktrace is not responsible so I don't think this is strictly an improvement.