RFR: 8266666: Implementation for snippets [v5]

[liach]

On Wed, 28 Jul 2021 14:40:55 GMT, Pavel Rappo <prappo at openjdk.org> wrote:

>> This PR implements JEP 413 "Code Snippets in Java API Documentation", which hasn't been yet proposed to target JDK 18. The PR starts as a squashed merge of the https://github.com/openjdk/jdk-sandbox/tree/jdk.javadoc/snippets branch.
>
> Pavel Rappo has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Change AnnotatedText<T> to StyledText
>    
>    Renames the class, removes its generic parameter, and changes the related terminology from "annotate" to "style".
>  - Restructure ...toolkit.taglets.snippet.** packages
>    
>    This commit moves the contents of the jdk.javadoc.internal.doclets.toolkit.taglets.snippet.{action,parser,text} packages into the jdk.javadoc.internal.doclets.toolkit.taglets.snippet package.

src/jdk.javadoc/share/classes/jdk/javadoc/internal/doclets/toolkit/taglets/snippet/Action.java line 37:

> 35:  * deletion without notice.</b>
> 36:  */
> 37: // FIXME: uncomment /* sealed */ when minimum boot version >= 17

Do we still have to wait? Currently `java.lang.reflect.Executable` and `java.lang.constant.ClassDesc` are already sealed. I wonder if uncommenting here is fine.

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