RFR: 8295653: Add a graph of the sealed class hierarchy for marked classes [v6]

[Magnus Ihse Bursie]

> It would be possible to mark classes with `@sealedGraph` to indicate that the sealed hierarchy should be rendered graphically in the JavaDocs. Classes not marked would be unaffected, creating an opt-in approach.
> 
> [Here](https://bugs.openjdk.org/secure/attachment/101126/Screen%20Shot%202022-10-19%20at%2012.47.47%20PM.png) is an example of MemoryLayout class rendering.
> 
> This feature has been developed in cooperation with Per Minborg.

Magnus Ihse Bursie has updated the pull request incrementally with two additional commits since the last revision:

 - Fix imports
 - Fix typo

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/10761/files
  - new: https://git.openjdk.org/jdk/pull/10761/files/b63decab..053e0e65

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10761&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10761&range=04-05

  Stats: 6 lines in 2 files changed: 2 ins; 1 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/10761.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10761/head:pull/10761

PR: https://git.openjdk.org/jdk/pull/10761