RFR: 8315999: Improve Date toString performance [v7]

[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 incrementally with two additional commits since the last revision:

 - improved DateTimeFormatter.format
 - improved ISO_INSTANT format

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/15658/files
  - new: https://git.openjdk.org/jdk/pull/15658/files/26d7c7c0..8b3f0637

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15658&range=06
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15658&range=05-06

  Stats: 459 lines in 6 files changed: 393 ins; 44 del; 22 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