<i18n dev> RFR: JDK-8317372: Refactor some NumberFormat tests to use JUnit

[Justin Lu]

Please review this PR which refactors a number of tests under `test/text/NumberFormat` to use JUnit.

During the switch to JUnit, the tests had the following updates (to improve readability)
- separate the test data generation from the actual execution of the test
- create distinct test methods so that all the tests aren't just run under one big method (e.g. main)

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Commit messages:
 - trailing ws
 - Clarify data provider for BigDecimalCompatibilityTest.java
 - initial commit

Changes: https://git.openjdk.org/jdk/pull/16035/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16035&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8317372
  Stats: 942 lines in 9 files changed: 389 ins; 200 del; 353 mod
  Patch: https://git.openjdk.org/jdk/pull/16035.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16035/head:pull/16035

PR: https://git.openjdk.org/jdk/pull/16035