MPLUGIN-421: Migrate legacy plugin Javadoc annotations

[wilx]

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Summary

Replace the remaining legacy @parameter and @required Javadoc tags in the plugin-report integration-test fixture with @Parameter metadata.

The rest of this fixture was migrated to maven-plugin-annotations in MPLUGIN-527, but the field-level tags were left behind. This change completes that conversion while preserving the required project.build.directory property expression. The fixture already has the annotation dependency, so no POM change is needed.

The generated descriptor contains:

<outputDirectory implementation="java.io.File">${project.build.directory}</outputDirectory>

This is an integration-test fixture cleanup and does not change production runtime behavior.

Related to #718.

Validation

The complete seven-module reactor and all integration tests passed on JDK 21 with both supported Maven lines:

Apache Maven 3.9.16:       mvn -B -V -Prun-its verify
Apache Maven 4.0.0-rc-6:  mvn -B -V -Prun-its verify

For each run, all 12 maven-plugin-report-plugin integration tests passed, including fix-maven-since-3.x. The plugin-plugin matrix passed 28 fixtures and skipped only the fixture intended for the other Maven major version.