RFR: 8315999: Improve Date toString performance

[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

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Commit messages:
 - improve date toString performance, includes:

Changes: https://git.openjdk.org/jdk/pull/15658/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15658&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315999
  Stats: 663 lines in 12 files changed: 574 ins; 7 del; 82 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