RFR: 8315585: Optimization for decimal to string [v3]

[Shaojin Wen]

> I submitted PR #15555 before, and there were too many changes. I split it into multiple PRs with small changes. This one is one of them.
> 
> this PR removed the duplicate code for getChars in BigDecimal#StringBuilderHelper, i also make performance faster.
> Please review and don't hesitate to critique my approach and patch.

Shaojin Wen has updated the pull request incrementally with one additional commit since the last revision:

  fix from @cl4es 's review

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/16006/files
  - new: https://git.openjdk.org/jdk/pull/16006/files/05406d99..72824dd5

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16006&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16006&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/16006.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16006/head:pull/16006

PR: https://git.openjdk.org/jdk/pull/16006