Fix armor stands disappearing when falling off sub-levels

[JpegN]

New ArmorStandMixin mirrors the minecart fix: when an armor stand is in a sub-level and not on the ground, kick it back to world space instead of letting it fall through shipyard and eventually get killed by the leave-plot tag. Server-only.

destroy_when_leaving_plot.json no longer needs the armor stand entry.

[JpegN]

I've found extra issues caused by my fix, will attempt to work them out.

[JpegN]

Armor stands can now land on sublevels and actually 'attach' to them, this fixes almost all issues.
If someone does a lot of weird interactions with an armor stand going on and off a sublevel it could still fail and disappear, but for normal play this should be absolutely fine. (someone smarter than me could probably resolve it completely but I'm not that person)

Fixes issue #877.

[Derpgamer22]

omg let's go :D

I do want to ask... would this work with supplementaries' hat stands? (The hat stand would have to have the tag that lets them retain on a sublevel would have to be given to them)

Also, since with this, armor stands would attach themselves to the sublevel when they fall on it... I wonder if it would be possible to have an armor stand on a sublevel with frost walker turn water into ice in the actual world. I had this machine thing that would have my sublevel create ice under it by using armor stands that were on the sublevel... but not at the same time...

[JpegN]

omg let's go :D

I do want to ask... would this work with supplementaries' hat stands? (The hat stand would have to have the tag that lets them retain on a sublevel would have to be given to them)

Also, since with this, armor stands would attach themselves to the sublevel when they fall on it... I wonder if it would be possible to have an armor stand on a sublevel with frost walker turn water into ice in the actual world. I had this machine thing that would have my sublevel create ice under it by using armor stands that were on the sublevel... but not at the same time...

This specific fix will not do anything for supplementaries' hat stand as is, or anything similar for that matter, I built it specifically on armor stands. Though it could be generalized to allow for easier compatibility, there were plenty of edge cases with the armor stand so I wouldn't be surprised to see even more with other similar entities.

As for the frostwalker thing, it will require a frostwalker-specific feature to be made to allow for the enchantment to work between sublevel and local world. That would be something for a feature request rather than a fix.

[Derpgamer22]

Ah alright, well I do want to say that if this PR does get accepted, if there could be compat added for supplementaries' hat stand with this by the team