RFR: 8315999: Improve Date toString performance [v8]

[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 incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 18 additional commits since the last revision:

 - merge from master & revert DateTimeFormatterBuilder
 - Merge branch 'master' into optim_for_date_to_string_2
   
   # Conflicts:
   #	src/java.base/share/classes/java/lang/StringUTF16.java
   #	src/java.base/share/classes/jdk/internal/util/DecimalDigits.java
 - improved DateTimeFormatter.format
 - improved ISO_INSTANT format
 - revert un-related changes
 - revert un-related changes
 - revert un-related changes
 - rebase PR #15651 last version
 - base PR #15651 API
 - move java.lang.StringLatin1::getChars to jdk.internal.util.DecimalDigits::getCharsLatin1
 - ... and 8 more: https://git.openjdk.org/jdk/compare/1cd96ce2...9040ea0c

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/15658/files
  - new: https://git.openjdk.org/jdk/pull/15658/files/8b3f0637..9040ea0c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15658&range=07
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15658&range=06-07

  Stats: 1245 lines in 45 files changed: 528 ins; 609 del; 108 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