Ractor: revert to moving object bytes, but size pool aware

Using `rb_obj_clone` introduce other problems, such as `initialize_*`
callbacks invocation in the context of the parent ractor.

So we can revert back to copy the content of the object slots,
but in a way that is aware of size pools.

bootstraptest/test_ractor.rb

@@ -2101,3 +2101,24 @@ assert_equal 'ok', %q{
     :fail
   end
 }
+
+# move objects inside frozen containers
+assert_equal 'ok', %q{
+  ractor = Ractor.new { Ractor.receive }
+  obj = Array.new(10, 42)
+  original = obj.dup
+  ractor.send([obj].freeze, move: true)
+  roundtripped_obj = ractor.take[0]
+  roundtripped_obj == original ? :ok : roundtripped_obj
+}
+
+# move object with generic ivar
+assert_equal 'ok', %q{
+  ractor = Ractor.new { Ractor.receive }
+  obj = Array.new(10, 42)
+  obj.instance_variable_set(:@array, [1])
+
+  ractor.send(obj, move: true)
+  roundtripped_obj = ractor.take
+  roundtripped_obj.instance_variable_get(:@array) == [1] ? :ok : roundtripped_obj
+}