Add potion support to more entities

[APickledWalrus]

Problem

Currently, potion syntax does not support Area Effect Clouds or Arrows (that is, the projectiles themselves, in flight).
This was something I missed in my original rework of Skript's potion syntax.

Solution

I've reworked potion syntax, mainly ExprPotionEffect and ExprPotionEffects, to work with a new provider system designed to make supporting new "potion providers" easy. There are 3 default implementations:

• LivingEntityProvider
• ItemTypeProvider
• EntityProvider
  • This is the new behavior for Arrows/AoE clouds
  • These two classes have the exact same potion API, but no common interface :(
  • I instead made one and created an additional wrapper around those two to reduce duplication

There is also a "NullProvider" which is just a dummy class. Used to avoid excessive null checking for invalid types (which will cause a runtime error if encountered)

I've also fixed a small issue where remove all (in ExprPotionEffects) did not properly consider active/hidden effects for living entities.

Testing Completed

In-game testing for new supported providers.
Existing potion test is extremely thorough and did not reveal any issues with the new system.

Supporting Information

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Completes: none
Related: none
AI assistance: none