Remove sbt-dotty

[adpi2]

• Remove DottyPlugin
• Move DottyIDEPlugin to project/, just in case some people are still using it
• Move the scripted tests to the new sbt-test project

[smarter]

I still don't understand why this is needed.

[adpi2]

It is explained in the comments below

[adpi2]

// `extendedClassLoaderCache` is package private in package sbt
val cache = state.extendedClassLoaderCache

[adpi2]

https://github.com/sbt/sbt/blob/40870d3fa84b005f70042948d81d21b3aae2d820/main-command/src/main/scala/sbt/State.scala#L399

[adpi2]

I agree now that it would be easier if makeScalaInstance is public in sbt...

[smarter]

Ah I missed that, so can we make this method public in sbt? It seems like the only way to properly use ScalaInstance which is public. Otherwise our build could break at any update of sbt.

[adpi2]

sbt/sbt#6480

[bishabosha]

Something broke the classpaths for scala3-bootstrapped in this PR, it now uses the referenceVersion of scala3-library, and not the dottyNonBootstrappedVersion of scala3-library , this prevents us from breaking the tasty version.

When I break the Tasty version, the error I see when trying to run scala3-bootstrapped/scalac is

error while loading Typeable$package$,
class file scala/reflect/Typeable$package.class is broken, reading aborted with class dotty.tools.tasty.UnpickleException
TASTy signature has wrong version.
 expected: {majorVersion: 28, minorVersion: 0}
 found   : {majorVersion: 28, minorVersion: 0 [unstable release: 3]}

This TASTy file was produced by an unstable release.
To read this TASTy file, your tooling must be at the same version.
The TASTy file was produced by Scala 3.0.0-RC3.

So we see it is using the scala3-library_3.0.0-RC3