RFR: 8315585: Optimization for decimal to string [v12]

[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 with a new target base due to a merge or a rebase. The pull request now contains 15 commits:

 - merge from master
 - Merge remote-tracking branch 'upstream/master' into optim_decimal_to_string_x1
   
   # Conflicts:
   #	src/java.base/share/classes/java/math/BigDecimal.java
 - use JLA
 - update copyright info & comments
 - reduce duplicate code & code format & refactor benchmark case
 - Merge remote-tracking branch 'upstream/master' into optim_decimal_to_string_x1
 - remove JLA
 - recipe ("\1.\1\1")
 - Use StringConcatFactory.makeConcatWithConstants
 - use % calculate lowInt
 - ... and 5 more: https://git.openjdk.org/jdk/compare/4e8c0364...2074a0da

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

Changes: https://git.openjdk.org/jdk/pull/16006/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16006&range=11
  Stats: 526 lines in 6 files changed: 271 ins; 163 del; 92 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