RFR: 8256999: Add C2 intrinsic for Reference.refersTo and PhantomReference::refersTo

[Vladimir Kozlov]

JDK-8188055 added the function Reference.refersTo. For performance, the supporting native methods Reference.refersTo0 and PhantomReference.refersTo0 should be intrinsified by C2.

Initial patch was prepared by @fisk.

Tested hs-tier1-4. Added new compiler tests to test intrinsics.

Ran new test with Shenandoah. Found only one issue. As result I disable  PhantomReference::refersTo intrinsic for COOP+ Shenandoah combination. Someone from Shenandoah team have to test changes if that is enough.

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Commit messages:
 - 8256999: Add C2 intrinsic for Reference.refersTo and PhantomReference::refersTo

Changes: https://git.openjdk.java.net/jdk/pull/1425/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1425&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8256999
  Stats: 381 lines in 16 files changed: 242 ins; 61 del; 78 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1425.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1425/head:pull/1425

PR: https://git.openjdk.java.net/jdk/pull/1425