RFR: 8265684: implement Sealed Classes as a standard feature in Java, javadoc changes [v3]

[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 incrementally with one additional commit since the last revision:

  addressing review comments

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/3613/files
  - new: https://git.openjdk.java.net/jdk/pull/3613/files/7d0ba41c..dc1bd3fb

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=3613&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=3613&range=01-02

  Stats: 55 lines in 3 files changed: 52 ins; 0 del; 3 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