RFR: 8343453: Modernize FloatingDecimal tests

[Raffaello Giulietti]

Simplify tests.

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Commit messages:
 - Merge branch 'master' into 8343453
 - 8343453: Modernize FloatingDecimal tests

Changes: https://git.openjdk.org/jdk/pull/21840/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21840&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8343453
  Stats: 3124 lines in 3 files changed: 1 ins; 3089 del; 34 mod
  Patch: https://git.openjdk.org/jdk/pull/21840.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21840/head:pull/21840

PR: https://git.openjdk.org/jdk/pull/21840