Add PreserveFirstFoundResourceTransformer

[Goooler]

Closes #1357.

---

• CHANGELOG's "Unreleased" section has been updated, if applicable.

[Goooler]

Noted the breaking change in #1547, we can't set the strategy back as it fails the transformers.

https://scans.gradle.com/s/ul6xobwusbbwm/tests/overview?outcome=FAILED

[Goooler]

May need to add a new transformer to prevent duplicate files to fallback the case like GrimAnticheat/Grim#2229 (comment).

[Copilot]

Pull Request Overview

This PR adds a new PreserveFirstFoundResourceTransformer class that provides a way to handle duplicate resources by preserving only the first instance found. This is particularly useful when using the default DuplicatesStrategy.INCLUDE and wanting to ensure only the first found resource (typically from the project itself) is included in the final JAR.

Key changes:

• Implements a new transformer that tracks found resources and excludes subsequent duplicates
• Adds comprehensive functional tests to verify the transformer behavior
• Updates documentation to reference the new transformer

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
PreserveFirstFoundResourceTransformer.kt	New transformer implementation with resource tracking logic
TransformersTest.kt	Functional test verifying the transformer preserves first found resources
docs/configuration/merging/README.md	Documentation update referencing the new transformer
docs/changes/README.md	Changelog entry documenting the addition
api/shadow.api	API definition for the new transformer class