Support for source enum extension

[lukebemish]

In light of the recent discussion on discord -- this seems like a useful thing to have in-source support for, right?

Like interface injection, JST has to generate stubs occasionally here -- for the EnumProxy fields or parameter providing methods that enum extensions can use.

This PR is marked as a draft for now. It is blocked by:

• Matching MDG PR
• Matching NG PR
• Matching FML work
• Implementing IndexedEnum and company support
• Handle ambiguity with multiple ctors and make sure to pick the right one when grabbing indices for getParameter

In particular -- FML needs to handle cases where enum entries to be injected exist already gracefully, including handling ordering so that "dev env with source-injected plus runtime-injected-from-a-dependency enum entries" and "prod server being tested against" get the same enum ordering.

This system validates that the targeted class extends a provided interface (presumably, you'd pass it IExtensibleEnum for neoforge-mode, and nothing for "vanilla" mode).

One question I have -- I currently hard-code the EnumProxy class used in stubs. Should this be un-hard-coded as an argument or the like?

[neoforged-pr-publishing]

• Publish PR to GitHub Packages

[lukebemish]

Whoops, just realized I think there's some indexed-enum stuff or the like this needs to support, I'll add that to the TODO list too