RFR: JDK-8266431: Dual-Pivot Quicksort improvements (Radix sort)

[iaroslavski]

Sorting:

- adopt radix sort for sequential and parallel sorts on int/long/float/double arrays (almost random and length > 6K)
- fix tryMergeRuns() to better handle case when the last run is a single element
- minor javadoc and comment changes

Testing:
- add new data inputs in tests for sorting
- add min/max/infinity values to float/double testing
- add tests for radix sort

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Commit messages:
 - JDK-8266431: Dual-Pivot Quicksort improvements (Radix sort)
 - JDK-8266431: Dual-Pivot Quicksort improvements (Radix sort)
 - JDK-8266431: Dual-Pivot Quicksort improvements (Radix sort)

Changes: https://git.openjdk.java.net/jdk/pull/3938/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3938&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8266431
  Stats: 889 lines in 3 files changed: 718 ins; 46 del; 125 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3938.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3938/head:pull/3938

PR: https://git.openjdk.java.net/jdk/pull/3938