RFR: 8260517: implement Sealed Classes as a standard feature

[Vicente Romero]

Please review this PR that intents to make sealed classes a final feature in Java. This PR contains compiler and VM changes. In line with similar PRs, which has made preview features final, this one is mostly removing preview related comments from APIs plus options in test cases.

Thanks

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Commit messages:
 - Merge branch 'master' into JDK-8260517
 - Merge branch 'master' into JDK-8260517
 - fixing failing regression tests
 - JVM related changes
 - 8260517: Compiler implementation for Sealed Classes

Changes: https://git.openjdk.java.net/jdk/pull/3526/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3526&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8260517
  Stats: 450 lines in 56 files changed: 48 ins; 282 del; 120 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3526.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3526/head:pull/3526

PR: https://git.openjdk.java.net/jdk/pull/3526