RFR: 8266666: Implementation for snippets [v7]

[Jonathan Gibbons]

On Fri, 20 Aug 2021 18:50:44 GMT, Jonathan Gibbons <jjg at openjdk.org> wrote:

>> Pavel Rappo has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Pass through FIXMEs and TODOs
>>   
>>   Downgrades FIXMEs that do not mark *feature issues* to TODOs, or removes those FIXMEs completely. For example, unlike Style hierarchy, Action hierarchy won't benefit from becoming sealed. So the respective FIXME is removed.
>
> Generally impressive piece of work.

> @jonathan-gibbons, do we need to mention the semantic change to `com.sun.source.doctree.AttributeTree` in the release notes? Before this PR, `AttributeTree` used to only represent HTML attributes. After this PR has been integrated, that interface will also represent attributes of the standard doclet tags. (Currently, the only such tag is `{@snippet}`.)

It doesn't seem worth a release note ... we're just using the tree in more places ...

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PR: https://git.openjdk.java.net/jdk/pull/4795