Use monomorphic versions of in-place modifying methods

It's not possible to represent side-effects and the receiver type changing, however some type checkers may choose to perform weak updates based on the types passed to these methods and in these situations its useful to still use the original type variables and not method-bound ones.

Author: hjwylde

core/array.rbs

@@ -628,8 +628,8 @@ class Array[unchecked out Elem] < Object
   #     a #=>  ["", "b", "c!", "d!"]
   #
   # collect! is monomorphic because of RBS limitation.
-  def collect!: [U] () { (Elem item) -> U } -> ::Array[U]
-              | () -> ::Enumerator[Elem, ::Array[untyped]]
+  def collect!: () { (Elem item) -> Elem } -> self
+              | () -> ::Enumerator[Elem, self]
 
   # When invoked with a block, yields all combinations of length `n` of elements
   # from the array and then returns the array itself.

core/hash.rbs

@@ -776,7 +776,7 @@ class Hash[unchecked out K, unchecked out V] < Object
   #     h = { "a" => 100, "b" => 200 }
   #     h.replace({ "c" => 300, "d" => 400 })   #=> {"c"=>300, "d"=>400}
   #
-  def replace: [A, B] (Hash[A, B]) -> Hash[A, B]
+  def replace: (Hash[K, V]) -> self
 
   # Returns a new hash consisting of entries for which the block returns true.
   #
@@ -906,8 +906,8 @@ class Hash[unchecked out K, unchecked out V] < Object
   #
   # If no block is given, an enumerator is returned instead.
   #
-  def transform_keys!: () -> Enumerator[K, Hash[untyped, V]]
-                     | () { (K) -> K } -> Hash[K, V]
+  def transform_keys!: () -> Enumerator[K, self]
+                     | () { (K) -> K } -> self
 
   # Returns a new hash with the results of running the block once for every value.
   # This method does not change the keys.
@@ -935,8 +935,8 @@ class Hash[unchecked out K, unchecked out V] < Object
   #
   # If no block is given, an enumerator is returned instead.
   #
-  def transform_values!: () -> Enumerator[V, Hash[K, untyped]]
-                       | [A] () { (V) -> A } -> Hash[K, A]
+  def transform_values!: () -> Enumerator[V, self]
+                       | () { (V) -> V } -> self
 
   # Adds the contents of the given hashes to the receiver.
   #