[lworld] RFR: 8373375: [lworld] Remove Unsafe.make/finishPrivateBuffer [v2]

[Chen Liang]

> WIP, replacing make/finishPrivateBuffer with flat array operations, yet to figure out how to ensure UseArrayFlattening is always on...

Chen Liang 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:

 - Redundant if block per review
 - Merge branch 'lworld' of https://github.com/openjdk/valhalla into fix/buffer-removal
 - Merge branch 'lworld' of https://github.com/openjdk/valhalla into fix/buffer-removal
 - Missed test
 - Rollback breaking change
 - Remove private buffer

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

Changes:
  - all: https://git.openjdk.org/valhalla/pull/2018/files
  - new: https://git.openjdk.org/valhalla/pull/2018/files/cf3de78c..b58a8b4f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=2018&range=01
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=2018&range=00-01

  Stats: 15623 lines in 414 files changed: 8566 ins; 3773 del; 3284 mod
  Patch: https://git.openjdk.org/valhalla/pull/2018.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/2018/head:pull/2018

PR: https://git.openjdk.org/valhalla/pull/2018