[MNG-7793] Add generated-source metadata to Maven 4 APIs

[goutamadwant]

Fixes #9196

Summary

Add explicit generated-source metadata to Maven 4's source model and APIs so plugins can distinguish generated files without relying on directory naming conventions.

Implementation

• Add the generated attribute to org.apache.maven.api.model.Source.
• Expose generated state through SourceRoot.
• Add explicit generated-source registration through ProjectManager.
• Preserve the value through model XML, consumer POM, and legacy resource adapter paths.
• Keep existing and legacy source registration defaulting to non-generated.
• Preserve first-registration-wins behavior for duplicate source roots.

Verification

• mvn --batch-mode verify
• Focused API, implementation, and core module verification
• XML round-trip and consumer POM coverage
• Generated registration, duplicate registration, and legacy resource mutation coverage

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[gnodet]

We need to target Maven 4.1.0, hence the model version 4.2.0.

[goutamadwant]

Thanks @gnodet. Updated the generated field to target model version 4.2.0 and moved the corresponding XML round-trip and consumer POM coverage to the 4.2.0 namespace. Let me know if this looks good now.

[slachiewicz]

One more thing to address, please rebase and squash commits

[goutamadwant]

@slachiewicz Rebased onto the latest master and squashed the changes into a single signed commit. Thanks for the review.!

[gnodet]

The generated attribute is properly threaded through all layers — model (4.2.0+), API (SourceRoot.generated()), service (ProjectManager.addSourceRoot overload), implementation (DefaultSourceRoot, DefaultProjectManager, ConnectedResource), and serialization (XML round-trip, consumer POM).

Backward compatibility is maintained via the bridging constructor that defaults generated to false. The duplicate-check logic in DefaultProjectManager.addSourceRoot correctly uses scope+language+directory as the key (excluding generated), preserving first-registration-wins semantics. Tests cover all the interesting cases: generated registration, duplicate handling, legacy non-generated default, resource mutation preservation, and XML round-trip in the 4.2.0 namespace.

The model version targeting (4.2.0+) addresses the earlier review feedback.

This review was generated by an AI agent, Hermès on behalf of @gnodet.