Add AuxiliaryClassFiles in IncOptions

[adpi2]

Fixes #579

Add an AuxiliaryClassFiles member in IncOptions so that the ClassFileManager manages the files that are associated to class files. This will be used for Scala 3 (.tasty files), for Scala.js (.sjsir files) and for Scala Native (.nir files).

The auxiliaryClassFiles member in IncOptions is an array so that we can manage several type of files at the same time (for instance .tasty and .sjsir files). Its default value is an empty array because Scala 2 and Java don't need any.

The implementation for .tasty files is provided so that it can already be reused by sbt (sbt/sbt#6080) and also by Mill and Bloop.

[eed3si9n]

Could you exercise this from https://github.com/sbt/zinc/blob/develop/zinc/src/test/scala/sbt/inc/IncrementalCompilerSpec.scala or scripted test somehow?

[smarter]

Thanks for working on this!

The auxiliaryClassFiles member in IncOptions is an array so that we can manage several type of files at the same time (for instance .tasty and .sjsir files). Its default value is an empty array because Scala 2 and Java don't need any.
The implementation for .tasty files is provided so that it can already be reused by sbt (sbt/sbt#6080) and also by Mill and Bloop.

I wonder if besides .tasty we shouldn't also hardcode .sjsir and .nir by default, it shouldn't break anything and it means that mill/bloop/maven/... don't have to remember to do this themselves. /cc @sjrd

[sjrd]

I wonder if besides .tasty we shouldn't also hardcode .sjsir and .nir by default, it shouldn't break anything and it means that mill/bloop/maven/... don't have to remember to do this themselves.

We could do that. I don't have a strong opinion either way. If Zinc doesn't do it by default, sbt-scalajs and sbt-scala-native will keep doing it.

[sjrd]

Overall LGTM. I have a few comments.