RFR: 8265684: implement Sealed Classes as a standard feature in Java, javadoc changes [v9]

[Vicente Romero]

> Please review the javadoc related changes to make sealed classes a final feature in Java. The patch is mostly removing preview features related code that is not necessary anymore in javadoc.
> 
> TIA

Vicente Romero has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 10 commits:

 - manual merge with master
 - Merge branch 'master' into JDK-8265684
 - fixing indentation: review comment
 - Merge branch 'master' into JDK-8265684
 - addressing indentation issues
 - Merge branch 'master' into JDK-8265684
 - additional commit addressing review comments
 - addressing review comments
 - Merge branch 'master' into JDK-8265684
 - 8265684: implement Sealed Classes as a standard feature in Java, javadoc changes

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Changes: https://git.openjdk.java.net/jdk/pull/3613/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3613&range=08
  Stats: 179 lines in 17 files changed: 3 ins; 117 del; 59 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3613.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3613/head:pull/3613

PR: https://git.openjdk.java.net/jdk/pull/3613