RFR: 8260517: implement Sealed Classes as a standard feature in Java [v5]

[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. Please also review the related [CSR](https://bugs.openjdk.java.net/browse/JDK-8265090)
> 
> Thanks
> 
> note: this PR is related to [PR-3528](https://github.com/openjdk/jdk/pull/3528) and must be integrated after it.

Vicente Romero has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains ten additional commits since the last revision:

 - Merge branch 'master' into JDK-8260517
 - Merge branch 'master' into JDK-8260517
 - updating comment after review feedback
 - removing javax.lang.model changes
 - 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:
  - all: https://git.openjdk.java.net/jdk/pull/3526/files
  - new: https://git.openjdk.java.net/jdk/pull/3526/files/43e9cb5f..2744f615

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=3526&range=04
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=3526&range=03-04

  Stats: 506473 lines in 3844 files changed: 20558 ins; 483521 del; 2394 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