RFR: JDK-8250768: javac should be adapted to changes in JEP 12 [v11]

[Jan Lahoda]

> This is an update to javac and javadoc, to introduce support for Preview APIs, and generally improve javac and javadoc behavior to more closely adhere to JEP 12.
> 
> The notable changes are:
> 
>  * adding support for Preview APIs (javac until now supported primarily only preview language features, and APIs associated with preview language features). This includes:
>      * the @PreviewFeature annotation has boolean attribute "reflective", which should be true for reflective Preview APIs, false otherwise. This replaces the existing "essentialAPI" attribute with roughly inverted meaning.
>      * the preview warnings for preview APIs are auto-suppressed as described in the JEP 12. E.g. the module that declares the preview API is free to use it without warnings
>  * improving error/warning messages. Please see [1] for a list of cases/examples.
>  * class files are only marked as preview if they are using a preview feature. [1] also shows if a class file is marked as preview or not.
>  * the PreviewFeature annotation has been moved to jdk.internal.javac package (originally was in the jdk.internal package).
>  * Preview API in JDK's javadoc no longer needs to specify @preview tag in the source files. javadoc will auto-generate a note for @PreviewFeature elements, see e.g. [2] and [3] (non-reflective and reflective API, respectively). A summary of preview elements is also provided [4]. Existing uses of @preview have been updated/removed.
>  * non-JDK javadoc is also enhanced to auto-generate preview notes for uses of Preview elements, and for declaring elements using preview language features [5].
>  
>  Please also see the CSR [6] for more information.
>  
>  [1] http://cr.openjdk.java.net/~jlahoda/8250768/JEP12-errors-warnings-v6.html
>  [2] http://cr.openjdk.java.net/~jlahoda/8250768/jdk.javadoc.00/api/java.base/java/lang/Record.html
>  [3] http://cr.openjdk.java.net/~jlahoda/8250768/jdk.javadoc.00/api/java.compiler/javax/lang/model/element/RecordComponentElement.html
>  [4] http://cr.openjdk.java.net/~jlahoda/8250768/jdk.javadoc.00/api/preview-list.html
>  [5] http://cr.openjdk.java.net/~jlahoda/8250768/test.javadoc.00/
>  [6] https://bugs.openjdk.java.net/browse/JDK-8250769

Jan Lahoda has updated the pull request incrementally with one additional commit since the last revision:

  Fixing navigator for the PREVIEW page.

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/703/files
  - new: https://git.openjdk.java.net/jdk/pull/703/files/097ae3c1..61264fe4

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=703&range=10
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=703&range=09-10

  Stats: 4 lines in 2 files changed: 2 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/703.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/703/head:pull/703

PR: https://git.openjdk.java.net/jdk/pull/703