Scala 2.12 support

[densh]

2.12 is near the end of the development cycle. We need to extend our nscplugin to support it.

[densh]

Here is the initial list of things that need to be done here:

• Update port of scala.runtime to reflect recent changes in Remove the duplicate implem of hash codes for numbers. scala/scala#5110 and Simplify scala.runtime scala/scala#5098
• Add proper support for closures to NIR
• Test support for SAMs and how it works with FunctionPtrN

[zizhengtai]

Any update on this?