[jdk21u-dev] RFR: 8317372: Refactor some NumberFormat tests to use JUnit

[Andrew Lu]

I backport this for parity with 21.0.5-oracle.

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Commit messages:
 - Backport 9622de2aa89923b8444df093ae1c596bc336f14f

Changes: https://git.openjdk.org/jdk21u-dev/pull/782/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=782&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8317372
  Stats: 943 lines in 9 files changed: 390 ins; 195 del; 358 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/782.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/782/head:pull/782

PR: https://git.openjdk.org/jdk21u-dev/pull/782