[Scala3] Move OpaqueTypeSpec and DirectionSpec

[adkian-sifive]

Summary

OpaqueTypeSpec was hitting two errors in Scala 3:

class MaybeBoxed needs to be abstract, since:
it has 3 unimplemented members.
  // Members declared in chiselTests.experimental.OpaqueTypeSpec$.MaybeBoxed
  def boxed: Boolean = ???
  def underlying: T = ???
  
  // Members declared in chisel3.Record
  def elements: scala.collection.immutable.SeqMap[String, chisel3.Data] = ???

and

def underlying = elements.head._2
                 ^^^^^^^^^^^^^^^^
          Found:    chisel3.Data
          Required: T
          where:    T is a type in class Boxed with bounds <: chisel3.Data

Release Notes

OpaqueTypeSpec now supported in Scala 3

[adkian-sifive]

I think this should be ready to merge if it passes CI