JS implementation of Collections.kt, copied from the native implementation

[ianparkinson]

A simple implementation of Collections.min and Collections.max for JS.

This is a copy of the existing native implementation.

The JVM implementation instead uses java.util.Collections.min and java.util.Collections.max. However, the native/JS implementation should also work under JVM - would it be better to add this implementation to commonMain and remove the platform-specific implementations?

[ftomassetti]

Thank you!