RFR: 8337168: Optimize LocalDateTime.toString [v4]

[Shaojin Wen]

> The current LocalDateTime.toString implementation concatenates the toString results of date and time, which can be passed to StringBuilder to reduce additional object allocation and improve performance.

Shaojin Wen has updated the pull request incrementally with one additional commit since the last revision:

  Update src/java.base/share/classes/java/time/LocalTime.java
  
  Co-authored-by: Chen Liang <liach at openjdk.org>

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Changes:
  - all: https://git.openjdk.org/jdk/pull/20321/files
  - new: https://git.openjdk.org/jdk/pull/20321/files/e7c5bc69..f17ea04a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20321&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20321&range=02-03

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/20321.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20321/head:pull/20321

PR: https://git.openjdk.org/jdk/pull/20321