RFR: 8315999: Improve Date toString performance [v4]

[温绍锦]

> improve date toString performance, includes:
> 
> java.util.Date.toString
> java.util.Date.toGMTString
> java.time.Instant.toString
> java.time.LocalDate.toString
> java.time.LocalDateTime.toString
> java.time.LocalTime.toString

温绍锦 has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains ten commits:

 - rebase PR #15651 last version
 - base PR #15651 API
 - move java.lang.StringLatin1::getChars to jdk.internal.util.DecimalDigits::getCharsLatin1
 - remove duplicate stringSize
 - update related comments
 - none static import
 - move java.util.DecimalDigits to jdk.internal.util.DecimalDigits
 - fix LocalDate.getChars offset
 - improve date toString performance, includes:
   
   java.util.Date.toString
   java.util.Date.toGMTString
   java.time.Instant.toString
   java.time.LocalDate.toString
   java.time.LocalDateTime.toString
   java.time.LocalTime.toString

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

Changes: https://git.openjdk.org/jdk/pull/15658/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15658&range=03
  Stats: 766 lines in 17 files changed: 626 ins; 54 del; 86 mod
  Patch: https://git.openjdk.org/jdk/pull/15658.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15658/head:pull/15658

PR: https://git.openjdk.org/jdk/pull/15658