add Array#flatten micro

Author: Nicolas Laurent

bench/micro/array/flatten-recursive.rb

@@ -0,0 +1,19 @@
+# Copyright (c) 2020 Oracle and/or its affiliates. All rights reserved. This
+# code is released under a tri EPL/GPL/LGPL license. You can use it,
+# redistribute it and/or modify it under the terms of the:
+#
+# Eclipse Public License version 2.0, or
+# GNU General Public License version 2, or
+# GNU Lesser General Public License version 2.1.
+
+array = []
+current_array = array
+100.times do
+  next_array = []
+  current_array.append(0, 1, next_array, 3, 4)
+  current_array = next_array
+end
+
+benchmark 'core-array-flatten-recursive' do
+  array.flatten
+end

bench/micro/array/flatten-simple.rb

@@ -0,0 +1,13 @@
+# Copyright (c) 2020 Oracle and/or its affiliates. All rights reserved. This
+# code is released under a tri EPL/GPL/LGPL license. You can use it,
+# redistribute it and/or modify it under the terms of the:
+#
+# Eclipse Public License version 2.0, or
+# GNU General Public License version 2, or
+# GNU Lesser General Public License version 2.1.
+
+array = [ [[1, 2], [3,4]], [[5,6], [7,8]] ]
+
+benchmark 'core-array-flatten-simple' do
+  array.flatten
+end