[RFC] Create a module that can compile and run Ammonite and scala-cli scripts

[lefou]

This related to com-lihaoyi/Ammonite#1228, which is worth a full read to understand the motivation

We need a module, that can

• read an Ammonite or scala-cli script,
• inspect it's magic imports,
• collects all included files (when Ammonite script),
• resolved it's dependencies (in one go),
• compiles all files,
• and provided a way to run the script
  • as Ammonite script
  • as Mill script
  • as scala-cli script

Once this is ready, we can stop using Ammonite for all of these tasks and can use this module to provide better BSP support.

[hilcode]

Seems like a good idea. The less magic, the better.

[lefou]

It might be worth to evaluate, if we can adapt the using directive (https://scala-cli.virtuslab.org/docs/guides/configuration#in-scala-and-sc-files) from Scala-cli for Mill build scripts. It seems to be much easier to parse them from Mill.

[lefou]

• Remove Ammonite as a dependency, handle script running and bootstrapping ourselves #2377
• Unify MillBuildModule with MillBuildRootModule #2414