Merge pull request scala/scala#7019 from szeiger/issue/10988

Make mutable Sets and Maps their own Builders

Author: lrytz

library/src/scala/collection/mutable/Map.scala

@@ -55,9 +55,12 @@ trait MapOps[K, V, +CC[X, Y] <: MapOps[X, Y, CC, _], +C <: MapOps[K, V, CC, C]]
   extends IterableOps[(K, V), Iterable, C]
     with collection.MapOps[K, V, CC, C]
     with Cloneable[C]
+    with Builder[(K, V), C]
     with Growable[(K, V)]
     with Shrinkable[K] {
 
+  def result(): C = coll
+
   @deprecated("Use - or remove on an immutable Map", "2.13.0")
   @deprecatedOverriding("This method should be final, but is not due to scala/bug#10853", "2.13.0")
   /*final*/ def - (key: K): C = clone() -= key

library/src/scala/collection/mutable/Set.scala

@@ -19,9 +19,11 @@ trait Set[A]
 trait SetOps[A, +CC[X], +C <: SetOps[A, CC, C]]
   extends collection.SetOps[A, CC, C]
     with Cloneable[C]
+    with Builder[A, C]
     with Growable[A]
     with Shrinkable[A] {
 
+  def result(): C = coll
 
   def add(elem: A): Boolean =
     !contains(elem) && {