feat: Support Groovy 6 changes to GroovyDoc (closes #381)

[keeganwitt]

No description provided.

[Copilot]

Pull request overview

This PR extends GMavenPlus GroovyDoc generation to support newer Groovy (Groovy 6+) behavior by adding new GroovyDoc options (e.g., syntax highlighter/theme, additional stylesheets) and introducing a preLanguage configuration that triggers Groovy’s PreLanguageRewriter post-processing.

Changes:

• Add new GroovyDoc Mojo parameters and wire them into GroovyDoc properties, plus copy support for additional stylesheets.
• Add preLanguage to GroovyDocConfiguration and propagate it from the Mojo into GroovyDoc generation.
• Add/extend unit tests around property setup, preLanguage propagation, and additional stylesheet handling.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
src/test/java/org/codehaus/gmavenplus/mojo/AbstractGroovyDocMojoTest.java	Adds tests for new GroovyDoc properties, preLanguage propagation, and additional stylesheet copying.
src/main/java/org/codehaus/gmavenplus/util/GroovyCompiler.java	Invokes Groovy 6 PreLanguageRewriter after GroovyDoc generation when configured.
src/main/java/org/codehaus/gmavenplus/mojo/AbstractGroovyDocMojo.java	Adds new GroovyDoc parameters, includes them in doc properties, copies additional stylesheets, and passes preLanguage into configuration.
src/main/java/org/codehaus/gmavenplus/model/GroovyDocConfiguration.java	Adds a preLanguage field with getter/setter for forked/in-process GroovyDoc generation.

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