RFR: 8258588: MD5 MessageDigest in java.util.UUID should be cached

[PROgrm_JARvis]

Please review this change moving lookup of MD5 digest in `java.lang.UUID` to an internal holder class.

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Commit messages:
 - 8258588: MD5 MessageDigest in java.util.UUID should be cached

Changes: https://git.openjdk.java.net/jdk/pull/1821/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1821&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8258588
  Stats: 33 lines in 1 file changed: 26 ins; 6 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1821.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1821/head:pull/1821

PR: https://git.openjdk.java.net/jdk/pull/1821