2026-May-05 - 2.7.15471

Introduce build convention plugins for common project setup  (#14311)

* Introduce build convention plugins for common project setup

Extracts shared Gradle configurations from the root `build.gradle.kts` `subprojects` block into dedicated convention plugins.

This refactoring centralizes reusable build logic for:
*   `triplea-test-conventions`: JUnit Platform, test logging, custom test output, and JaCoCo.
*   `triplea-base-project`: Java compiler options, Checkstyle, and PMD. This plugin also applies `triplea-test-conventions`.
*   `triplea-java-application`: Applies the `application` plugin and `triplea-base-project`.
*   `triplea-java-library`: Applies `java-library`, Spotless, and `triplea-base-project`.

This approach reduces boilerplate and improves modularity, reducing the need for extensive `subprojects` configuration and keeping project setup more local and explicit.

* Update build documentation for convention plugins

Expands the overview of Gradle convention plugins by providing detailed descriptions for each plugin's purpose, applied plugins, and specific configurations (e.g., Java 21, Spotless, Jacoco).

* Restore mistakenly commented out test