RFR: 8352565: Add native method implementation of Reference.get() [v2]

[Kim Barrett]

> Please review this change which adds a native method providing the
> implementation of Reference::get.  Referece::get is an intrinsic candidate, so
> this native method implementation is only used when the intrinsic is not.
> 
> Currently there is intrinsic support by the interpreter, C1, C2, and graal,
> which are always used.  With this change we can later remove all the
> per-platform interpreter intrinsic implementations, and might also remove the
> C1 intrinsic implementation.
> 
> Testing:
> (1) mach5 tier1-6 normal (so using all the existing intrinsics).
> (2) mach5 tier1-6 with interpreter and C1 Reference::get intrinsics disabled.

Kim Barrett has updated the pull request incrementally with one additional commit since the last revision:

  parameterized return type of native get0

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/24315/files
  - new: https://git.openjdk.org/jdk/pull/24315/files/f1734062..37dc9b74

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=24315&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=24315&range=00-01

  Stats: 4 lines in 1 file changed: 0 ins; 2 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/24315.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24315/head:pull/24315

PR: https://git.openjdk.org/jdk/pull/24315