RFR: 8313621: test/jdk/jdk/internal/math/FloatingDecimal/TestFloatingDecimal should use RandomFactory

[Brian Burkhalter]

Change test to use `RandomFactory` instead of `new Random()` and convert it to JUnit 5.

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Commit messages:
 - 8313621: Convert test to JUnit 5
 - 8313621: test/jdk/jdk/internal/math/FloatingDecimal/TestFloatingDecimal should use RandomFactory

Changes: https://git.openjdk.org/jdk/pull/16130/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16130&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8313621
  Stats: 118 lines in 1 file changed: 11 ins; 78 del; 29 mod
  Patch: https://git.openjdk.org/jdk/pull/16130.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16130/head:pull/16130

PR: https://git.openjdk.org/jdk/pull/16130