RFR: 8338745: Intrinsify Continuation.pin() and Continuation.unpin() [v3]

[Markus Grönlund]

> Greetings,
> 
> Please help review this change set that implements C2 intrinsics for jdk.internal.vm.Continuation.pin() and jdk.internal.vm.Continuation.unpin().
> 
> This work is a consequence of [JDK-8338417](https://bugs.openjdk.org/browse/JDK-8338417), which required us to introduce explicit pin constructs for Virtual threads in a relatively performance-sensitive path.
> 
> Testing: jdk_jfr, loom testing
> 
> Comment: I changed the type of the ContinuationEntry::_pin_count field from uint to uin32_t to make the size explicit and to access it uniformly from the intrinsic code using T_INT.
> 
> Thanks
> Markus

Markus Grönlund has updated the pull request incrementally with one additional commit since the last revision:

  JVMCI exportation

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Changes:
  - all: https://git.openjdk.org/jdk/pull/20664/files
  - new: https://git.openjdk.org/jdk/pull/20664/files/fa9a737a..ba68f2c2

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20664&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20664&range=01-02

  Stats: 4 lines in 2 files changed: 4 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/20664.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20664/head:pull/20664

PR: https://git.openjdk.org/jdk/pull/20664