Continue to complete PR #16006 to improve performance and reduce duplicate code
------------- Commit messages: - optimize BigDecimal toString/toPlainString - add benchmark Changes: https://git.openjdk.org/jdk/pull/22009/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22009&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8315585 Stats: 391 lines in 3 files changed: 188 ins; 121 del; 82 mod Patch: https://git.openjdk.org/jdk/pull/22009.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/22009/head:pull/22009 PR: https://git.openjdk.org/jdk/pull/22009
