Adds new spawn reasons for 1.21

[EquipableMC]

Description

This simply adds support for ominous item spawner for spawn reasons, which was approved very recently in #10897 in paper.

Edit:
This also adds support for potion effects, which was approved the day before paper 1.21 became stable in #11102

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Target Minecraft Versions: 1.21
Requirements: 1.21 paper
Related Issues:

[TheLimeGlass]

There is now also potion effect as a spawn reason as of Yesterday, the day before Paper released 1.21. Can that be added here?

[EquipableMC]

There is now also potion effect as a spawn reason as of Yesterday, the day before Paper released 1.21. Can that be added here?

yeah, I'll add it now

[APickledWalrus]

might be worth testing how this interacts with like:

set {_var} to some potion effect
if {_var} is a potion effect:

[EquipableMC]

might be worth testing how this interacts with like:

set {_var} to some potion effect
if {_var} is a potion effect:

oh yeah good call let me test now

[APickledWalrus]

some quick testing indicates that for:

set {_var} to some potion effect
if {_var} is a potion effect:

it works fine for a potion effect, not for potion effect. i don't imagine this would have a major impact (and this is already likely an issue with other types).