RFR: 8260517: implement Sealed Classes as a standard feature in Java [v3]

[Maurizio Cimadamore]

On Fri, 16 Apr 2021 03:35:06 GMT, Vicente Romero <vromero at openjdk.org> wrote:

>> 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 incrementally with one additional commit since the last revision:
> 
>   updating comment after review feedback

Compiler changes look good (I have not checked SymbolGenerator).

Why were some tests removed?

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Marked as reviewed by mcimadamore (Reviewer).

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