[MPLUGIN-421] Replace QDox with JavaParser for Javadoc extraction

[wilx]

Summary

Replace the annotation extractor's QDox-backed Java source model with JavaParser and its symbol solver. This fixes descriptor generation for comment-only Java source files while retaining Javadoc extraction, reference resolution, and link generation.

Fixes #718.

Implementation

• Add a JavaParser source model that resolves project sources, reactor output directories, dependency JARs, and the complete Java class library.
• Port Mojo and parameter Javadoc extraction, member lookup, static-field values, module lookup, and internal/external link resolution from QDox to JavaParser.
• Keep directory and JAR classpath entries visible through one class loader with platform-module delegation.
• Add regression coverage for comment-only sources, mixed reactor/JAR inheritance, JDK platform modules, generated sources, and observable source-root exclusion.
• Remove the annotation extractor's direct QDox dependency and update the dependency diagram.

The user-visible result is that valid projects containing a .java file with only comments no longer fail during the descriptor goal. Existing Javadoc metadata and links continue to be generated through the new model.

Validation

• JAVA_HOME=/opt/jdks/latest-17 mvn spotless:apply
• JAVA_HOME=/opt/jdks/latest-17 mvn -Prun-its verify
  • Maven Plugin Plugin ITs: 31 passed, 1 Maven-version-specific test skipped
  • Maven Plugin Report Plugin ITs: 12 passed

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