[lworld] RFR: 8348599: [lworld] Unsafe.getValue() and Unsafe.putValue() have expensive lookup code

[Frederic Parain]

New version of Unsafe methods to read and write flat values.
More details in the CR.

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

Commit messages:
 - New Unsafe get/put method with LayoutKind argument

Changes: https://git.openjdk.org/valhalla/pull/1336/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1336&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8348599
  Stats: 258 lines in 3 files changed: 242 ins; 0 del; 16 mod
  Patch: https://git.openjdk.org/valhalla/pull/1336.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1336/head:pull/1336

PR: https://git.openjdk.org/valhalla/pull/1336