<i18n dev> RFR: 8345818: Fix SM cleanup of parsing of System property resource.bundle debug

[Roger Riggs]

Replace broken getProperty with Boolean.getBoolean.

Manual testing confirms trace messages are enabled with `-Dresource.bundle.debug=true`

-------------

Commit messages:
 - 8345818: Fix SM cleanup of parsing of System property resource.bundle.debug

Changes: https://git.openjdk.org/jdk/pull/22649/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22649&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8345818
  Stats: 2 lines in 1 file changed: 0 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/22649.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22649/head:pull/22649

PR: https://git.openjdk.org/jdk/pull/22649