RFR: 8188044: We need Math.unsignedMultiplyHigh [v3]

[Brian Burkhalter]

> Please consider this proposal to add a method `unsignedMultiplyHigh(long,long)` to each of `java.lang.Math` and `java.lang.StrictMath`.

Brian Burkhalter has updated the pull request incrementally with one additional commit since the last revision:

  8188044: Use multiplyHigh() to gleverage the inverage the intrinsic

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4644/files
  - new: https://git.openjdk.java.net/jdk/pull/4644/files/0a8fec63..2ad5e395

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4644&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4644&range=01-02

  Stats: 20 lines in 2 files changed: 9 ins; 5 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4644.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4644/head:pull/4644

PR: https://git.openjdk.java.net/jdk/pull/4644