RFR: 8283698: Refactor Locale constructors used in src/test

[Naoto Sato]

This is a follow-on task after deprecating the Locale constructors (https://bugs.openjdk.java.net/browse/JDK-8282819). Most of the changes are simple replacements to Locale constructors with `Locale.of()` or Locale constants, such as `Locale.US`.

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Commit messages:
 - 8283698: Refactor Locale constructors used in src/test

Changes: https://git.openjdk.java.net/jdk/pull/8130/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8130&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8283698
  Stats: 750 lines in 182 files changed: 3 ins; 3 del; 744 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8130.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8130/head:pull/8130

PR: https://git.openjdk.java.net/jdk/pull/8130