Gradle plugin adds generated sources JAR to end of the test classpath

[sbrannen]

As discussed in #1265 (comment), the AOT testing support in the Gradle plugin currently adds the *-aot-test.jar (containing generated sources and resources) to the end of the original test classpath.

This results in generated code not being able to override existing code.

For example, the generated SpringFactoriesLoader appears on the classpath after the standard SpringFactoriesLoader present in the spring-core JAR, which means that the standard SpringFactoriesLoader support is used instead of the AOT generated one that uses StaticSpringFactories.