RFR: 8308753: Class-File API transition to Preview [v16]

[Adam Sotona]

> Classfile API is an internal library under package `jdk.internal.classfile` in JDK 21.
> This pull request turns the Classfile API into a preview feature and moves it into `java.lang.classfile`.
> It repackages all uses across JDK and tests and adds lots of missing Javadoc.
> 
> This PR goes in sync with [JDK-8308754](https://bugs.openjdk.org/browse/JDK-8308754): Class-File API (Preview) (CSR)
> and [JDK-8280389](https://bugs.openjdk.org/browse/JDK-8280389): Class-File API (Preview) (JEP).
> 
> Online javadoc is available at: 
> https://cr.openjdk.org/~asotona/JDK-8308753-preview/api/java.base/java/lang/classfile/package-summary.html
> 
> In addition to the primary transition to preview, this pull request also includes:
> - All Classfile* classes ranamed to ClassFile* (based on JEP discussion).
> - A new preview feature, `CLASSFILE_API`, has been added.
> - Buildsystem tool required a little patch to support annotated modules.
> - All JDK modules using the Classfile API are newly participating in the preview.
> - All tests that use the Classfile API now have preview enabled.
> - A few Javac tests not allowing preview have been partially reverted; their conversion can be re-applied when the Classfile API leaves preview mode.
> 
> Despite the number of affected files, this pull request is relatively straight-forward. The preview version of the Classfile API is based on the internal version of the library from the JDK master branch, and there are no API features added.
> 
> Please review this pull request to help the Classfile API turn into a preview.
> 
> Any comments are welcome.
> 
> Thanks,
> Adam

Adam Sotona has updated the pull request incrementally with two additional commits since the last revision:

 - removed AttributeMapper::validSince
 - fixed DirectCodeBuilder

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/15706/files
  - new: https://git.openjdk.org/jdk/pull/15706/files/7fe5db2b..21f4bb03

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15706&range=15
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15706&range=14-15

  Stats: 105 lines in 25 files changed: 47 ins; 30 del; 28 mod
  Patch: https://git.openjdk.org/jdk/pull/15706.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15706/head:pull/15706

PR: https://git.openjdk.org/jdk/pull/15706