RFR: 8277013: Allow creation of module graphs without defining modules to the VM

[Ivan Ristović]

Related JBS issue: https://bugs.openjdk.java.net/browse/JDK-8277013

The GraalVM Native Image module support must create the runtime boot-module layer at image build time; module instances created at build time need to reflect module relations at runtime, i.e., their opens, reads, and exports. To achieve this, we had to duplicate and modify a significant portion of the module synthesis methods from the JDK. The GraalVM PR that demonstrates this duplication can be found at:
  ​https://github.com/oracle/graal/blob/9bfa3a312d7d0309eb014d52e49afd7136d9e77e/substratevm/src/com.oracle.svm.hosted.jdk11/src/com/oracle/svm/hosted/ModuleLayerFeature.java#L269

The hard-to-maintain code duplication is necessary as synthesizing module graphs in the JDK unconditionally defines modules to the VM which causes an error due to module redefinition. For example, methods `System.defineModule`, `ModuleLayer` factories and constructor, and `Module` constructor unconditionally update the VM state. All these methods eventually reach the `Module` constructor or the `Modules.defineModules` method.

We propose that the `Module` constructor and the `Modules.defineModules` conditionally update the VM state (similarly to 'Module.implAddReads`). The JDK would call these methods so they update the VM state and GraalVM Native Image would call them without updating the state.

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Commit messages:
 - Update parameter names; Add constructor overload for backward compatibility
 - Enhance Module.defineModules to accept switches to update VM state

Changes: https://git.openjdk.java.net/jdk/pull/6356/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6356&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8277013
  Stats: 52 lines in 1 file changed: 36 ins; 0 del; 16 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6356.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6356/head:pull/6356

PR: https://git.openjdk.java.net/jdk/pull/6356