RFR: 8268611: jar --validate should check targeted classes in MR-JAR files [v3]

[Christian Stein]

> Please review this change ensuring all targeted classes in a MR-JAR file should target the same or a lower classfile version. The [JAR File Specification](https://docs.oracle.com/javase/9/docs/specs/jar/jar.html#Multi-release) of JavaSE 9 reads:
> 
>> A class file under a versioned directory, of version N say, in a multi-release JAR must have a class file version less than or equal to the class file version associated with Nth major version of a Java platform release.
> 
> For example, having compiled source files with `javac` 25 without using the `--release` option (or with `--release 25`) and trying to archive them via a `jar --create --file a.jar --release 9 ... --release 10 ...` command now fails with:
> 
> classfile release value of META-INF/versions/9/version/Version.class too high: 25
> classfile release value of META-INF/versions/10/version/Version.class too high: 25
> invalid multi-release jar file a.jar deleted
> 
> 
> This pull request contains fixes to existing tests which produced invalid MR-JAR files. Most of those fixes are achieved by adding an appropriate `--release N` option to the associated `javac` call. One of those fixes rewrites the classfile version bytes between the `javac` and `jar` calls.

Christian Stein has updated the pull request incrementally with one additional commit since the last revision:

  Remove the informal "(Java N)" clause.

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/22103/files
  - new: https://git.openjdk.org/jdk/pull/22103/files/d889660c..1170fd9e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=22103&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=22103&range=01-02

  Stats: 3 lines in 2 files changed: 0 ins; 1 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/22103.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22103/head:pull/22103

PR: https://git.openjdk.org/jdk/pull/22103