[11u] RFR 8225715: jhsdb jmap fails to write binary heap dump of a jshell process

[Aleksey Shipilev]

Original bug:
  https://bugs.openjdk.java.net/browse/JDK-8225715
  https://hg.openjdk.java.net/jdk/jdk/rev/f60890de1dfb

The patch does not apply cleanly to 11u, because we miss quite large JDK-8205534 that changed the
context by adding "names" HashSet. Fortunately, the patch can be re-applied by hand in an obvious
manner. The test is not affected.

11u webrev:
  https://cr.openjdk.java.net/~shade/8225715/webrev.11u.01/

Testing: new test (fails without product fix, passes with it); tier1

-- 
Thanks,
-Aleksey