RFR: 8265130: Make ConstantDesc class hierarchy sealed [v2]

[Gavin Bierman]

> Hi all,
> 
> Please review this patch to make the ConstantDesc hierarchy `sealed`, as was promised in its Javadoc, now that sealed classes are finalising in JDK 17. 
> 
> Thanks,
> Gavin

Gavin Bierman has updated the pull request incrementally with one additional commit since the last revision:

  Removing javadoc comments about future use of sealed

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4135/files
  - new: https://git.openjdk.java.net/jdk/pull/4135/files/8084e90b..1cd54624

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4135&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4135&range=00-01

  Stats: 131 lines in 6 files changed: 102 ins; 29 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4135.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4135/head:pull/4135

PR: https://git.openjdk.java.net/jdk/pull/4135