Implement forEach in Collections.CopiesList

Originally was proposed by Zheka Kozlov here: http://mail.openjdk.java.net/pipermail/core-libs-dev/2018-December/057192.html

Just a tiny optimization: we can use for-i loop instead of Iterable.forEach() which is relying on iterator.

Benchmarking demonstrates good improvement, see https://github.com/openjdk/jdk/pull/2524