Update for nullable spawner types, `editMeta` util (#2514)
* Add `ItemProperty#editMeta` util
* Update & cleanup `ItemTag.spawner_type`
* Cleanup `ItemInstrument` and use `editMeta`
* Minor cleanup
* Support unsetting the instrument
* Minor cleanup
* `spawnerType` -> `spawnedType`
* Update `LocationTag` ones, make it 1.20+
* Correct no mech input check
* Use a direct cast
* Remove workaround for now fixed Spigot bug
(
commit: 890a0b6)
