Implement Lingering potion & Area Effect Cloud

[IvanCraft623]

Introduction

Implements lingering potions and area effect cloud + custom effect support, also complements #5163

Changes

API changes

• The following new classes have been added:
  • entity\effect\EffectContainer
  • pocketmine\entity\object\AreaEffectCloud
  • pocketmine\item\LingeringPotion
• The following API methods have changed signatures
  • SplashPotion->setLinger() - now returns self instead of void

Rationale for EffectContainer addition

Unlike entities (Living) there are different types of things that can contain effects that are not necessarily applied. Such is the case of AreaEffectCloud.

Other stuff that may contain effects:

• Potion:

  PocketMine-MP/src/item/Potion.php

  Line 63 in d5762d3

  //TODO: check CustomPotionEffects NBT

• Tipped arrows

Backwards compatibility

No BC-breaking changes.

Tests

https://youtu.be/cRAjwEVbb0w
This has been playtested and and there was only one issue:

• On fire animation is shown when extinguishing fire (this is an already known bug on PM).

[dktapps]

Nice, I'll review this tomorrow.

[IvanCraft623]

Minecraft Bedrock implements AreaCloudEffect in a weird way, behaves differently than described in the wiki and in java.
Some examples:

• The number of times the effect is applied varies per effect (I still can't figure out the criteria).
• Regardless of where the SplashPotion falls, the cloud will be positioned in the middle of the block.
• ReapplicationDelay changes depending if the effect is Instantaneous.
• RadiusOnUse is applied even the cloud has no effects.
• The potion effect is stored in the ListTag effects, it does not make sense since it is aready storing the PotionId.
• It is only updated every 10 ticks.

[dktapps]

This PR is rather bloated by the EffectContainer changes so it's difficult for me to see what's going on. I've given this only a cursory review.