Deprecate lowcode language loader for removal

[shartte]

One can now make lowcode mods by simply using the javafml language loader and not providing any java classes at all.

Once #246 is implemented, it will be much more natural to just not define a language loader at all for datapack-style mods, and that makes the lowcode loader somewhat redundant, which is why I suggest we deprecate it for removal (or outright remove it in a BC).
The guidance for modders should be: Just remove the loader + loaderversion from your neoforge.mods.toml.

There is slight overhead of creating a mod event bus even for such mods that don't have any event subscribers, but in large modpacks, datpack mods will make up a tine fraction of the overall mods, so I do not anticipate negative effects because of this.

[TelepathicGrunt]

Does this need to be a BC and just not treat any pre-existing mod setup as lowcode like a normal mod out of box without them needing to change?

[shartte]

We could translate the lowcode loader to javafml automatically and print a warning, yeah.