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

[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.

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Commit messages:
 - 8265828: [TestBug] Save and restore the default Locale in javafx.base unit test LocalDateTimeStringConverterTest

Changes: https://git.openjdk.org/jfx/pull/954/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=954&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8265828
  Stats: 16 lines in 1 file changed: 13 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