RFR: 8315585: Optimization for decimal to string [v2]

[Shaojin Wen]

> Continue to complete PR #16006 and PR #21593 to improve BigDecimal::toString and BigDecimal::toPlainString performance and reduce duplicate code

Shaojin Wen has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 27 commits:

 - copyright
 - Merge remote-tracking branch 'upstream/master' into dec_to_str_202501
   
   # Conflicts:
   #	src/java.base/share/classes/jdk/internal/util/DecimalDigits.java
 - simplify and comments
 - simplify
 - simplify
 - code style
 - revert change
 - bug fix
 - bug fix
 - refactor
 - ... and 17 more: https://git.openjdk.org/jdk/compare/d985b31c...0e7b30be

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Changes: https://git.openjdk.org/jdk/pull/23310/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23310&range=01
  Stats: 388 lines in 3 files changed: 239 ins; 54 del; 95 mod
  Patch: https://git.openjdk.org/jdk/pull/23310.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23310/head:pull/23310

PR: https://git.openjdk.org/jdk/pull/23310