RFR: 8295653: Add a graph of the sealed class hierarchy for marked classes [v2]

[Jonathan Gibbons]

On Thu, 20 Oct 2022 11:13:18 GMT, Magnus Ihse Bursie <ihse at openjdk.org> wrote:

>> 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 one additional commit since the last revision:
> 
>   Fix styleheet

make/jdk/src/classes/build/tools/taglet/SealedGraph.java line 49:

> 47: public final class SealedGraph implements Taglet {
> 48:     private static final String sealedGraphDotPath =
> 49:             System.getProperty("sealedGraphDotPath");

Generally, there is strong correlation between the module graph support and the sealed graph support, which is good, and helpful.   This system property is an outlier. For consistency with the world of module graphs, it should be `enableSealedGraph` or something like that.  Related: a change in the property name here will require a corresponding update in the makefiles.

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