RFR: 8265684: implement Sealed Classes as a standard feature in Java, javadoc changes [v6]

[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 incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains seven additional commits since the last revision:

 - 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

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/3613/files
  - new: https://git.openjdk.java.net/jdk/pull/3613/files/846d34b5..436a75c6

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=3613&range=05
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=3613&range=04-05

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