<i18n dev> RFR: 8300818: Reduce complexity of padding with DateTimeFormatter

[Sergey Tsypanov]

Currently it's O(n) - we do `n` shifts of bytes within `StringBuilder`. This can be reduced to O(1) improving the code like:

DateTimeFormatter dtf = new DateTimeFormatterBuilder()
  .appendLiteral("Date:")
  .padNext(20, ' ')
  .append(DateTimeFormatter.ISO_DATE)
  .toFormatter();
String text = dtf.format(LocalDateTime.now());

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Commit messages:
 - Improve padding of DateTimeFormatter

Changes: https://git.openjdk.org/jdk/pull/12131/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12131&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8300818
  Stats: 5 lines in 1 file changed: 0 ins; 2 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/12131.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12131/head:pull/12131

PR: https://git.openjdk.org/jdk/pull/12131