RFR: JDK-8310502 : Optimization for j.l.Long.fastUUID() [v26]

[温绍锦]

> By optimizing the implementation of java.lang.Long#fastUUID, the performance of the java.util.UUID#toString method can be significantly improved.
> 
> The following are the test results of JMH: 
> 
> Benchmark                     Mode  Cnt      Score      Error   Units
> UUIDUtilsBenchmark.new       thrpt    5  92676.550 ±  292.213  ops/ms
> UUIDUtilsBenchmark.original  thrpt    5  37040.165 ± 1023.532  ops/ms

温绍锦 has updated the pull request incrementally with one additional commit since the last revision:

  fix UUID.java import, rename jdk.util.HexDigits to jdk.util.Hex256 and make private constructor.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/14578/files
  - new: https://git.openjdk.org/jdk/pull/14578/files/6b61a715..9fe1d705

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14578&range=25
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14578&range=24-25

  Stats: 35 lines in 3 files changed: 4 ins; 5 del; 26 mod
  Patch: https://git.openjdk.org/jdk/pull/14578.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14578/head:pull/14578

PR: https://git.openjdk.org/jdk/pull/14578