RFR: JDK-8329118: Run MessageFormat additional subformat pattern tests under en_US locale [v2]

[Justin Lu]

> Please review this PR which updates two MessageFormat sub format related tests to be guaranteed to run under the `en_US` locale.
> 
> There exists locale that do not provide distinct instances for separate styles. For example, the `en_IN` locale provides the same LONG and SHORT compact number instances. The test data is built to test sub formats under the assumption that different styles do provide distinct instances.
> 
> As this is the case, these tests should be ran under a locale that does provide distinct instances for separate styles.

Justin Lu has updated the pull request incrementally with one additional commit since the last revision:

  implement suggestions

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Changes:
  - all: https://git.openjdk.org/jdk/pull/18498/files
  - new: https://git.openjdk.org/jdk/pull/18498/files/1ea2cd4e..33dc70ab

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18498&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18498&range=00-01

  Stats: 26 lines in 2 files changed: 9 ins; 4 del; 13 mod
  Patch: https://git.openjdk.org/jdk/pull/18498.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18498/head:pull/18498

PR: https://git.openjdk.org/jdk/pull/18498