Move to using architectury, support neoforge platform

[onebeastchris]

Note: This PR targets this Floodgate branch: https://github.com/GeyserMC/Floodgate/tree/core-repackage - it just repackages floodgate's core module into a package suffixed by .core. Otherwise, NeoForge complains about it shipping a package that clashes with geyser-common. hurray.

Changes made:

• Yeeted Jenkinsfile as we plan to move away from it anyways; modrinth would be used to upload floodgate fabric/neoforge artifacts
• replaces resource loading via classloader with the mod calls to load files from jar's
• adds build-logic plugins, similar to how they're in hydraulic/geyser/floodgate already

Most code can be shared between the two platforms, which is neat. One curiousity of neoforge is that it has its own event when (plugin message) listeners are registered, which this PR accounts for by starting the floodgate plugin message module only once we're able to register those.

TODO

• [x] modrinth uploading changes, similar to https://github.com/GeyserMC/Geyser/pull/4989

[onebeastchris]

modded-floodgate.zip Here are the floodgate-neoforge and fabric-neoforge builds produced by this PR