Changes

SPIGOT-5345: Add automatic library support

Example plugin.yml usage:
```
    libraries:
      - com.squareup.okhttp3:okhttp:4.9.0
```

Libraries will only be accessible to plugins and their transitive depends, allowing for multiple versions of the same library to be used by different plugins.

This feature is modeled on the parallel BungeeCord feature and intends to offer the same behaviour.
Although this is a preview feature, major changes to behaviour are not expected at this point.

With the exception of the issues described in SPIGOT-6419 it is not expected that this feature alters classloading behaviour, although some changes may be unavoidable.