RFR: 8300818: Reduce complexity of padding with DateTimeFormatter [v3]

[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());

Sergey Tsypanov 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 six additional commits since the last revision:

 - Merge branch 'master' into dtfb
 - 8300818: Add benchmark
 - 8300818: Add benchmark
 - Revert irrelevant change
 - Merge branch 'master' into dtfb
 - Improve padding of DateTimeFormatter

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/12131/files
  - new: https://git.openjdk.org/jdk/pull/12131/files/322ae9b4..b40de5a8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12131&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12131&range=01-02

  Stats: 497235 lines in 5533 files changed: 277601 ins; 160858 del; 58776 mod
  Patch: https://git.openjdk.org/jdk/pull/12131.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/12131/head:pull/12131

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