RFR: 8220732: setSeed(long) java api doc is missing warning about provided seed quality

[Kevin Driver]

Resolves [JDK-8220732](https://bugs.openjdk.org/browse/JDK-8220732?filter=42718). The additional guidance as been added to the javadoc for `setSeed(long)`

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Commit messages:
 - Resolves JDK-8220732. The additional guidance as been added to the javadoc for setSeed(long)

Changes: https://git.openjdk.org/jdk/pull/9156/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=9156&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8220732
  Stats: 5 lines in 1 file changed: 5 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/9156.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9156/head:pull/9156

PR: https://git.openjdk.org/jdk/pull/9156