RFR: 8333133: Simplify QuickSort::sort

[Kim Barrett]

The "idempotent" argument is removed from that function, with associated
simplifications to the implementation. Callers are updated to remove that
argument. Callers that were providing a false value are unaffected in their
behavior.  The 3 callers that were providing a true value to request the
associated feature are also unaffected (other than by being made faster),
because the arrays involved don't contain any equivalent pairs.

There are also some miscellaneous cleanups, including using the swap utility
and fixing some comments.

Testing: mach5 tier1-3

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Commit messages:
 - remove idempotent

Changes: https://git.openjdk.org/jdk/pull/19464/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19464&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8333133
  Stats: 125 lines in 11 files changed: 3 ins; 95 del; 27 mod
  Patch: https://git.openjdk.org/jdk/pull/19464.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19464/head:pull/19464

PR: https://git.openjdk.org/jdk/pull/19464