[glaforge]

Summary

This PR adds a groupArtifact option to PalantirJavaFormatStep (spotless-lib), PalantirJavaFormatConfig (spotless-plugin-gradle), and PalantirJavaFormat (spotless-plugin-maven), bringing palantirJavaFormat to parity with googleJavaFormat (#944) and cleanthat.

Motivation & Use Cases

In #3084, a proposal to add a brand-new openJavaFormat formatter step (~490 lines) was closed because a fork of palantir-java-format is not differentiated enough to warrant its own separate top-level entry in the Spotless table of contents.

However, Spotless already has a clean, idiomatic pattern for supporting binary-compatible forks or custom Maven coordinates without adding new entries to the table of contents: the groupArtifact option (as supported by GoogleJavaFormatStep since #944 and CleanthatJavaStep).

Currently, PalantirJavaFormatStep hardcodes com.palantir.javaformat:palantir-java-format, which prevents Maven and Gradle users from pointing palantirJavaFormat at:

1. dev.openjavaformat:open-java-format (21.0.2+), which is binary-compatible with Spotless's existing PalantirJavaFormatFormatterFunc glue (including JavaFormatterOptions.Style.PALANTIR, restored in openjavaformat/open-java-format#200).
2. Internal corporate builds or patched forks of palantir-java-format hosted under custom Maven coordinates.

With this small change, users can seamlessly configure open-java-format (or any binary-compatible fork) using the existing palantirJavaFormat step:

Gradle:

spotless {
  java {
    palantirJavaFormat('21.0.2').groupArtifact('dev.openjavaformat:open-java-format')
  }
}

Maven:

<palantirJavaFormat>
  <groupArtifact>dev.openjavaformat:open-java-format</groupArtifact>
  <version>21.0.2</version>
</palantirJavaFormat>

Changes

• lib: Add PalantirJavaFormatStep.defaultGroupArtifact() and PalantirJavaFormatStep.create(String groupArtifact, String version, String style, boolean formatJavadoc, Provisioner provisioner) with groupId:artifactId validation (matching GoogleJavaFormatStep). Keep PalantirJavaFormatStep.MAVEN_COORDINATE intact for backwards compatibility.
• plugin-gradle: Add groupArtifact(String) to JavaExtension.PalantirJavaFormatConfig and document in plugin-gradle/README.md.
• plugin-maven: Add @Parameter private String groupArtifact to PalantirJavaFormat and document in plugin-maven/README.md.
• tests: Add unit and integration tests across testlib, plugin-gradle, and plugin-maven (including formatting with dev.openjavaformat:open-java-format:21.0.2 on JDK 21+ and testing groupArtifact validation and SerializableEqualityTester).
• changelogs: Updated CHANGES.md, plugin-gradle/CHANGES.md, and plugin-maven/CHANGES.md.