RFR: 8333893: Optimization for StringBuilder append boolean & null [v20]

[Shaojin Wen]

> After PR https://github.com/openjdk/jdk/pull/16245, C2 optimizes stores into primitive arrays by combining values ​​into larger stores.
> 
> This PR rewrites the code of appendNull and append(boolean) methods so that these two methods can be optimized by C2.

Shaojin Wen 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 26 additional commits since the last revision:

 - Merge remote-tracking branch 'origin/optim_str_builder_append_202406' into optim_str_builder_append_202406
 - fix build error
 - Merge remote-tracking branch 'upstream/master' into optim_str_builder_append_202406
 - Merge remote-tracking branch 'upstream/master' into optim_str_builder_append_202406
 - Merge remote-tracking branch 'origin/optim_str_builder_append_202406' into optim_str_builder_append_202406
 - Merge remote-tracking branch 'upstream/master' into optim_str_builder_append_202406
 - Merge remote-tracking branch 'upstream/master' into optim_str_builder_append_202406
 - revert test
 - Merge remote-tracking branch 'upstream/master' into optim_str_builder_append_202406
 - Merge remote-tracking branch 'upstream/master' into optim_str_builder_append_202406
 - ... and 16 more: https://git.openjdk.org/jdk/compare/2370f48a...457735c9

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/19626/files
  - new: https://git.openjdk.org/jdk/pull/19626/files/ae054771..457735c9

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19626&range=19
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19626&range=18-19

  Stats: 90483 lines in 1658 files changed: 73190 ins; 9277 del; 8016 mod
  Patch: https://git.openjdk.org/jdk/pull/19626.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19626/head:pull/19626

PR: https://git.openjdk.org/jdk/pull/19626