scalafix-rules_3 (GSoC 2022)

[rvacaru]

Follows #1629
Part of the issues #1583 and #1680

Ready for review:

• moved rules ExplicitResultTypes (with all related dependencies) and ProcedureSyntax in scala-2
  • did not check if also other rules should be moved to scala-2
• provided another TPrintImplicits in scala-3, exact copy as the one in scala-2.12+
• added rules3/compile in ci-3 check

[bjaglin]

rebased against #1629 to ease the review

[bjaglin]

Nice!

We'll have to reflect on how to have different versions of https://github.com/scalacenter/scalafix/blob/main/scalafix-rules/src/main/resources/META-INF/services/scalafix.v1.Rule based on the scala version, as the presence of the reference to a non-existing ProcedureSyntax will cause a runtime failure for

scalafix/scalafix-core/src/main/scala/scalafix/internal/v1/Rules.scala

Lines 101 to 108 in d6645da

	def all(classLoader: ClassLoader): List[Rule] = {
	import scala.jdk.CollectionConverters._
	ServiceLoader
	.load(classOf[Rule], classLoader)
	.iterator()
	.asScala
	.toList
	}

But this can be handled later, when working on unit3.