RFR: 8265828: [TestBug] Save and restore the default Locale in javafx.base unit test LocalDateTimeStringConverterTest [v3]

[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 with a new target base due to a merge or a rebase. The pull request now contains four commits:

 - Merge branch 'master' of https://git.openjdk.org/jfx into JDK-8265828-locale
 - Refactor remaining LocalStringConverter tests
   
   Treatment done in this commit is similar to the previous change.
 - LocalDateTimeStringConverterTest: Refactor test to properly utilize Locale
   
   * Locale initialization was moved to @BeforeClass method.
   * DateTimeFormatter objects are allocated after Locale initialization
   * Since LocalDateTimeStringConverter depends on DateTimeFormatter and on VM's Locale,
     creation of it was moved to @Before method.
 - 8265828: [TestBug] Save and restore the default Locale in javafx.base unit test LocalDateTimeStringConverterTest

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Changes: https://git.openjdk.org/jfx/pull/954/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=954&range=02
  Stats: 268 lines in 3 files changed: 207 ins; 21 del; 40 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