Great Registry Repackaging

[apple502j]

Resolves #3002

Since this snapshot's changes mean people have to change imports anyway, why not do it now?

And question to folks: should we make subpackages? and if so how?

[Shnupbups]

Not that I oppose it exactly, but why repackage tag to registry/tag?

[apple502j]

Tags are now managed by the registry (since 1.18.2).

[haykam821]

Could entry and entry list classes be placed into a separate package?

[Bixilon]

this PR can't be serious...

[md5]

Placing the entry classes in a separate package results in this error when trying to bootstrap during a JUnit test:

java.lang.IllegalAccessError: class net.minecraft.registry.SimpleRegistry tried to access method 'void net.minecraft.registry.entry.RegistryEntry$Reference.setRegistryKey(net.minecraft.registry.RegistryKey)' (net.minecraft.registry.SimpleRegistry and net.minecraft.registry.entry.RegistryEntry$Reference are in unnamed module of loader 'app')

It looks like the fabric-loader-junit package allows me to get past that error, so perhaps it doesn't matter all that much for my use case, but I thought I'd bring it up since this mapping is resulting code that tries to access a package private member across package boundaries.