Introduce support for processing test contexts ahead-of-time

[snicoll]

NBT allows to invoke an existing test suite in a native image. For that to work, we need to process each test context ahead-of-time and make sure that the optimized version is available in the classpath that NBT uses.

The underlying feature is being implemented in the core framework. See spring-projects/spring-framework#28825 which should provide a main class to invoke similar to our AotProcessor.

Things to consider:

• Create a test mojo in the Maven Plugin that invokes the main class as part of the process-test-classes phase. As part of this work, some of the code in the existing AotGenerateMojo can be refactored to be reused (typically the bits that do the compilation and copying).
• Create a new Gradle task that invokes the main class
• Update the native maven profile to include a call to the new mojo. This is worth a discussion as the testing with native bit could be totally opt-in. Perhaps it could be added but skipped by default with a way to enable it using a property?

Naming wise, we started a discussion in #31918.

Sub Tasks:

• Add Maven plugin support for processing test contexts ahead-of-time #32191
• Add Gradle plugin support for processing test contexts ahead-of-time #32192
• Introduce a nativeTest maven profile #32383
• Update SpringBootContextLoader to support AOT #31965

[sbrannen]

For an overview of the current status of native testing support in the TestContext framework, see:

• Implement GraalVM native image support in the TestContext framework spring-framework#29029

[philwebb]

Closing this one as superseded since all the sub-tasks have now been closed.