[8u] RFR 8214687: Optimize Collections.nCopies().hashCode() and equals()

[Aleksey Shipilev]

Original RFE:
  https://bugs.openjdk.java.net/browse/JDK-8214687
  https://hg.openjdk.java.net/jdk/jdk/rev/cfceb4df2499

Patch applies with usual reshufflings. But the test parts require touchups to compile and run on 8u:
type inference is not that rich, and there is no Objects.checkIndex. 8u webrev:
  https://cr.openjdk.java.net/~shade/8214687/webrev.8u.01/

Testing: tier1-like suite, new test

-- 
Thanks,
-Aleksey