fix(core/patcher): incremental compilation

[Floppy012]

Fixes #199 by modifying the classpath and adding the path to the already compiled classes as first entry. This way the compiler loads all the patched classes instead of the original ones from the dependencies. The classpath modification only takes place when compileJava runs an incremental compile.

I initially tried to use Machine Maker's filtered jar but then noticed that the same problem occurs with classes from external libs such as brigadier.

I have not found anything over the last day that would let me solve this in another (less-hacky) way.

I'm also not that familiar with kotlin & gradle so I'm not really familiar with best-practices. If there is anything wrong feel free to @ me or to fix it yourself 😄

(This could also be placed directly in the paper-server build config. Let me know what you prefer)