RFR: 8311302: Allow for jlinking a custom runtime without packaged modules being present [v22]

[Severin Gehwolf]

> Please review this patch which adds a jlink mode to the JDK which doesn't need the packaged modules being present. A.k.a run-time image based jlink. Fundamentally this patch adds an option to use `jlink` even though your JDK install might not come with the packaged modules (directory `jmods`). This is particularly useful to further reduce the size of a jlinked runtime. After the removal of the concept of a JRE, a common distribution mechanism is still the full JDK with all modules and packaged modules. However, packaged modules can incur an additional size tax. For example in a container scenario it could be useful to have a base JDK container including all modules, but without also delivering the packaged modules. This comes at a size advantage of `~25%`. Such a base JDK container could then be used to `jlink` application specific runtimes, further reducing the size of the application runtime image (App + JDK runtime; as a single image *or* separate bundles, depending on the app b
 eing modularized).
> 
> The basic design of this approach is to add a jlink plugin for tracking non-class and non-resource files of a JDK install. I.e. files which aren't present in the jimage (`lib/modules`). This enables producing a `JRTArchive` class which has all the info of what constitutes the final jlinked runtime.
> 
> Basic usage example:
> 
> $ diff -u <(./bin/java --list-modules --limit-modules java.se) <(../linux-x86_64-server-release/images/jdk/bin/java --list-modules --limit-modules java.se)
> $ diff -u <(./bin/java --list-modules --limit-modules jdk.jlink) <(../linux-x86_64-server-release/images/jdk/bin/java --list-modules --limit-modules jdk.jlink)
> $ ls ../linux-x86_64-server-release/images/jdk/jmods
> java.base.jmod            java.net.http.jmod       java.sql.rowset.jmod      jdk.crypto.ec.jmod         jdk.internal.opt.jmod                     jdk.jdi.jmod         jdk.management.agent.jmod  jdk.security.auth.jmod
> java.compiler.jmod        java.prefs.jmod          java.transaction.xa.jmod  jdk.dynalink.jmod          jdk.internal.vm.ci.jmod                   jdk.jdwp.agent.jmod  jdk.management.jfr.jmod    jdk.security.jgss.jmod
> java.datatransfer.jmod    java.rmi.jmod            java.xml.crypto.jmod      jdk.editpad.jmod           jdk.internal.vm.compiler.jmod             jdk.jfr.jmod         jdk.management.jmod        jdk.unsupported.desktop.jmod
> java.desktop.jmod         java.scripting.jmod      java.xml.jmod             jdk.hotspot.agent.jmod     jdk.internal.vm.compiler.manage...

Severin Gehwolf has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 90 commits:

 - Fix race wrt. first and second image generation.
   
   The second, create-linkable-runtime enabled link, needs to depend
   on the first (default jdk link). Also fix an issue with respect to
   which support dir is being used for which link.
 - Merge branch 'master' into jdk-8311302-jmodless-link
 - Fix comment.
 - Review feedback and Windows build fix (FixPath)
 - Fix comment in autoconf file
 - Remove no longer needed plugin options
 - Restore GenerateJLIClassesPluginTest.java
 - Update some comments
 - Add copyright header/comments
 - Ensure build-only plugin isn't propagated to the final image
 - ... and 80 more: https://git.openjdk.org/jdk/compare/fc0472ba...e25dd440

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Changes: https://git.openjdk.org/jdk/pull/14787/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14787&range=21
  Stats: 3549 lines in 38 files changed: 3413 ins; 111 del; 25 mod
  Patch: https://git.openjdk.org/jdk/pull/14787.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14787/head:pull/14787

PR: https://git.openjdk.org/jdk/pull/14787