Specialization's duplicator loses annotations

[scabug]

$ cat Z.scala 
object Test {
  class myAnnotation extends scala.annotation.StaticAnnotation
  def dontForgetTheAnnotation_![@specialized(Int) X](x: X) = {
    @myAnnotation val y = 3
  }
}

$ scalac Z.scala -Xprint:spec
[[syntax trees at end of                specialize]] // Z.scala
package <empty> {
  object Test extends Object {
    ...
    def dontForgetTheAnnotation_![@specialized(scala.Int) X >: Nothing <: Any](x: X): Unit = {
      @Test.myAnnotation val y: Int = 3;
      ()
    };
    <specialized> def dontForgetTheAnnotation_!$mIc$sp(x: Int): Unit = {
      val y: Int = 3; // @Test.annotation was lost during duplication
      ()
    }
  }
}

This prevents a full fix for #7344.

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-7579?orig=1
Reporter: @VladUreche
Affected Versions: 2.10.2-RC2

[scabug]

@VladUreche said:
Note to self: don't forget to enable the test case for #7344 when this is fixed.

[scabug]

@dragos said:
Another reason to stop removing annotations from the AST (the annotations are moved to the corresponding symbol during type-checking)...

[scabug]

@VladUreche said:
I agree it's annoying to copy annotations over in Duplicators, but having them attached to symbols makes any annotation change much easier, as there's no need to update the tree. So I guess it's Duplicators that should adapt, not the other way around.

On the other hand, I should really look into this, copying over annotations using the invalidSyms map only copied the annotations to skolems instead of the original type params, so there may be deeper bugs that need to be addressed. Or maybe it should only track skolems?

[scabug]

@VladUreche said:
Fixed in miniboxing => miniboxing/miniboxing-plugin@e6c92bb

In case there's serious interest in this bug, I can port it to scalac (right now, only Iuli and me are watching it...)