[21.2] Add more specialized DeferredRegister types

[ApexModder]

This pull request introduces new DeferredRegister and DeferredHolder types for various registries, streamlining the process of adding new elements.
Additionally, it includes a refactor that relocates everything under a deferred subpackage, causing this to target the next BC window.

[neoforged-pr-publishing]

• Publish PR to GitHub Packages

Last commit published: ac23d4aab70d57eb35b61450959771742043f781.

PR Publishing

The artifacts published by this PR:

• 📦 net.neoforged:neoforge:21.1.49-pr-1516-pr-extra-deferred-register
• 📦 net.neoforged:testframework:21.1.49-pr-1516-pr-extra-deferred-register

Repository Declaration

In order to use the artifacts published by the PR, add the following repository to your buildscript:

repositories {
    maven {
        name 'Maven for PR #1516' // https://github.com/neoforged/NeoForge/pull/1516
        url 'https://prmaven.neoforged.net/NeoForge/pr1516'
        content {
            includeModule('net.neoforged', 'neoforge')
            includeModule('net.neoforged', 'testframework')
        }
    }
}

MDK installation

In order to setup a MDK using the latest PR version, run the following commands in a terminal.
The script works on both *nix and Windows as long as you have the JDK bin folder on the path.
The script will clone the MDK in a folder named NeoForge-pr1516.
On Powershell you will need to remove the -L flag from the curl invocation.

mkdir NeoForge-pr1516
cd NeoForge-pr1516
curl -L https://prmaven.neoforged.net/NeoForge/pr1516/net/neoforged/neoforge/21.1.49-pr-1516-pr-extra-deferred-register/mdk-pr1516.zip -o mdk.zip
jar xf mdk.zip
rm mdk.zip || del mdk.zip

To test a production environment, you can download the installer from here.

[neoforged-compatibility-checks]

@ApexModder, this PR introduces breaking changes.
Unfortunately, this project is not accepting breaking changes right now.
Please revert them before this PR can be merged.
Last checked commit: ac23d4aab70d57eb35b61450959771742043f781.

neoforge (:neoforge)

• net/neoforged/neoforge/registries/DeferredRegister$Blocks
  • ❗ API class no longer exists
• net/neoforged/neoforge/registries/DeferredItem
  • ❗ API class no longer exists
• net/neoforged/neoforge/registries/DeferredRegister$Items
  • ❗ API class no longer exists
• net/neoforged/neoforge/registries/DeferredRegister$DataComponents
  • ❗ API class no longer exists
• net/neoforged/neoforge/registries/DeferredHolder
  • ❗ API class no longer exists
• net/neoforged/neoforge/registries/DeferredRegister
  • ❗ API class no longer exists
• net/neoforged/neoforge/registries/DeferredBlock
  • ❗ API class no longer exists

[neoforged-automation]

@ApexModder, this pull request has conflicts, please resolve them for this PR to move forward.