RFR: 8265684: implement Sealed Classes as a standard feature in Java, javadoc changes [v2]

[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 two additional commits since the last revision:

 - 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/2b7cee9e..7d0ba41c

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=3613&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=3613&range=00-01

  Stats: 38611 lines in 1297 files changed: 7670 ins; 26934 del; 4007 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