Extra API utilities

[ebo2022]

This PR contains a few things me and a few other people have found useful and would like to merge directly into Pollen for ease-of-access.

Here's the brief list:

• Modified "FollowBlock" and "FollowItem" classes that are able to "follow" a specified item in the creative inventory
• A new platform method ("areModsLoaded", including a toggle for whether all need to be present to return true
• A compostable registry so nobody has to dig into internals in the vanilla ComposterBlock
• A Flammable Registry, same as previous but applies to fire behavior
• GroupUtil class, used in FollowItem and FollowBlock for indexing the creative menu
• New TreeUtil class with utilities for creating a tree feature
• New DirectionalBlockPos class whose instance can store a BlockPos and a Direction
• New method in PollinatedBlockRegistry to generate a simple flower pot block

[ebo2022]

Update: Talked with Shock Micro, realized almost most of this is copied or derived from Blueprint (unknowingly; I was transferring from another library mod with a good amount of common code), so I understand if this doesn't comply with the standards for Pollen

[jacksonhardaway]

We'll be implementing some of the registries in this PR in the next minor update.