RFR (XS): CR 8003985: Support @Contended annotation

[Aleksey Shipilev]

Hi guys,

This is the JDK side of changes for supporting @Contended:
  http://cr.openjdk.java.net/~shade/8003985/webrev.jdk.02/

Status:
 - This change is ready to be pushed; due to licensing reasons with
jsr166, we can only commit the stub; regular jsr166 sync will bring the
updated annotation later.
 - JEP-142 is in Funded state (http://openjdk.java.net/jeps/142)
 - CCC is in place, and Approved.

I need a sponsor to push this.

Thanks,
-Aleksey.