…s/feather-protocol@a39d1f8

This is going to be a major change in how the crate structure is organized.
I'll explain more about this in future commits, once the refactor begins to take shape.

This crate generates a bunch of code from a variety of sources. It's intended to replace
`feather-definitions` and `feather-data`, to some extent.

I switched from Legion to hecs because:
* Legion's API is generally verbose and difficult to use in cases it wasn't
built for.
* Legion brings on unnecessary functionality, such as its systems scheduler, which is
bad impact on compile times.
* Legion doesn't support proper change detection. (Hecs doesn't either,
but right now I'm using Bevy's fork of it, which has change detection
in first-class.)

This ports the block code generator to 1.16 and the new crate layout.
I've changed it to ingest data from the Vanilla data report outputted
according to https://wiki.vg/Data_Generators.

Instead of taking data from feather-data, the generator now expects the
blocks report to have been manually generated in the current directory.
The benefit of this is that feather-data can be removed from the build process. I know many had
problems with the JDK and rustfmt requirements, so this simplifies things nicely.

Block code is no longer automatically generated at build time; now creating it
must be done manually. That said, it's cached in Git, so regenerating code
is only necessary when we upgrade to a new version.

This commit only ports the generator. What still needs to be done:
* Block categories, wall_blocks, directions
* SimplifiedBlockKind

feather-datapacks will replace feather-data as a solution for loot tables and recipes.
We download the vanilla JAR at startup, then extract the vanilla datapack for access
to whatever assets we need.

Looks like some IDs changed between 1.16.1 and 1.16.2.

This implements the initial plugin API.

The code is rough in some areas, especially the query code. There is some unsafe magic
that needs reviewing and cleaning up. But so far, the code seems to work.