Declaring a default adapter for all entrypoints of a mod

[liach]

So when mods are using custom entrypoint adapters, they need to declare the adapter for every entrypoint usage. However, it is quite likely that a mod would use a specific adapter for most of their entrypoints than using many different specific overrides (e.g. language-specific adapters, adapter that pass mod container instances to entrypoints if possible, adapter that reads a custom entrypoint notation). Thoughts?

This feature should be quite easy to implement, and I would volunteer if the idea is accepted and the json key is determined. I recommend defaultLanguageAdapter, so we may have:

{
  ...
  "defaultLanguageAdapter": "kotlin",
  "entrypoints": {
    "main": [
      // Now this is a list of class name than objects, way shorter
    ]
  }
}

It's just as simple as replacing

fabric-loader/src/main/java/net/fabricmc/loader/impl/metadata/V1ModMetadataParser.java

Line 282 in f1e0cc2

String adapter = "default";

to the new key's associated value.

@sfPlayer1 for evaluation.