Implement extractors for TASTY trees

* Define TASTY data types in scala.tasty
* Add method get a TASTY term from a quoted.Expr[T]
* Implement TASTY tree extractors

Use direct extractors for tasty trees

Workaround issue #4449

Rename TopLevelStatement to Tree

Author: nicolasstucki

compiler/src/dotty/tools/dotc/transform/Splicer.scala

@@ -48,7 +48,8 @@ object Splicer {
    */
   private def getLiftedArgs(call: Tree, bindings: List[Tree])(implicit ctx: Context): List[Any] = {
     val bindMap = bindings.map {
-      case vdef: ValOrDefDef => (vdef.rhs, ref(vdef.symbol).withPos(vdef.rhs.pos))
+      case vdef: ValDef => (vdef.rhs, ref(vdef.symbol).withPos(vdef.rhs.pos))
+      case ddef: DefDef => (ddef.rhs, ddef.rhs)
     }.toMap
     def allArgs(call: Tree, acc: List[List[Tree]]): List[List[Tree]] = call match {
       case call: Apply => allArgs(call.fun, call.args :: acc)

tests/pos/tasty/definitions.scala

@@ -39,12 +39,19 @@ object definitions {
   case class TypeDef(name: String, rhs: TypeTree | TypeBoundsTree) extends Definition {
     def mods: List[Modifier] = ???
   }
-  case class ClassDef(name: String, constructor: DefDef, parents: List[Term | TypeTree],
+  case class ClassDef(name: String, constructor: DefDef, parents: List[Parent],
                       self: Option[ValDef], body: List[Statement]) extends Definition {
     def mods: List[Modifier] = ???
   }
   case class PackageDef(name: String, members: List[Statement]) extends Definition
 
+// ------ Parents--------------------------------
+
+  enum Parent {
+    case TermParent(parent: Term)
+    case TypeParent(parent: TypeTree)
+  }
+
 // ------ Terms ---------------------------------
 
   /** Trees denoting terms */