RFR: 8265828: [TestBug] Save and restore the default Locale in javafx.base unit test LocalDateTimeStringConverterTest [v6]

[Lukasz Kostyra]

> The change moves Locale setting in the test to `@BeforeClass` and `@AfterClass` calls. `@BeforeClass` method call stores current default VM locale and applies Locale.US, while `@AfterClass` method restores old VM locale after all tests are completed.
> 
> I tested it both on Mac and Windows, in both cases Locale is changed, restored properly and tests pass.

Lukasz Kostyra has updated the pull request incrementally with one additional commit since the last revision:

  Remove unnecessary InvalidParameterException import

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Changes:
  - all: https://git.openjdk.org/jfx/pull/954/files
  - new: https://git.openjdk.org/jfx/pull/954/files/b1db3c0f..f0fa3760

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=954&range=05
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=954&range=04-05

  Stats: 3 lines in 3 files changed: 0 ins; 3 del; 0 mod
  Patch: https://git.openjdk.org/jfx/pull/954.diff
  Fetch: git fetch https://git.openjdk.org/jfx pull/954/head:pull/954

PR: https://git.openjdk.org/jfx/pull/954