RFR: 8253312: Enable JVM experiments in specialization under an opt-in mode

[Srikanth Adayapalam]

Early support for specialization experiements via type restrictions on fields.

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Commit messages:
 - 8253312: Enable JVM experiments in specialization under an opt-in mode

Changes: https://git.openjdk.java.net/valhalla/pull/199/files
 Webrev: https://webrevs.openjdk.java.net/?repo=valhalla&pr=199&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253312
  Stats: 311 lines in 17 files changed: 289 ins; 3 del; 19 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/199.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/199/head:pull/199

PR: https://git.openjdk.java.net/valhalla/pull/199