Hide old Tuple.toList and implement as extension

This should in theory be backwards TASTy compatible.

Fixes scala#12721

Author: nicolasstucki

library/src/scala/Tuple.scala

@@ -11,9 +11,8 @@ sealed trait Tuple extends Product {
   inline def toArray: Array[Object] =
     runtime.Tuples.toArray(this)
 
-  /** Create a copy this tuple as a List */
-  inline def toList[This >: this.type <: Tuple]: List[Union[This]] =
-    this.productIterator.toList.asInstanceOf[List[Union[This]]]
+  private[scala] inline def toList: List[Union[this.type]] =
+    this.productIterator.toList.asInstanceOf[List[Union[this.type]]]
 
   /** Create a copy this tuple as an IArray */
   inline def toIArray: IArray[Object] =
@@ -231,6 +230,11 @@ object Tuple {
 
   def fromProductTyped[P <: Product](p: P)(using m: scala.deriving.Mirror.ProductOf[P]): m.MirroredElemTypes =
     runtime.Tuples.fromProduct(p).asInstanceOf[m.MirroredElemTypes]
+
+  /** Create a copy this tuple as a List */
+  extension [This <: Tuple](inline tuple: This)
+    inline def toList: List[Union[This]] =
+      tuple.productIterator.toList.asInstanceOf[List[Union[This]]]
 }
 
 /** A tuple of 0 elements */