Add checks for factories files

META-INF/spring.factories and META-INF/spring/aot.factories in the
main source set are now checked. The checks verify that:

- Each class listed in the values exists in the source set's output
- The classes are listed alphabetically
- Nested classes are identified using their binary name

Closes gh-44676

spring-boot-project/spring-boot-test/src/main/resources/META-INF/spring/aot.factories

@@ -1,2 +1,2 @@
 org.springframework.beans.factory.aot.BeanFactoryInitializationAotProcessor=\
-org.springframework.boot.test.context.SpringBootContextLoader.MainMethodBeanFactoryInitializationAotProcessor
+org.springframework.boot.test.context.SpringBootContextLoader$MainMethodBeanFactoryInitializationAotProcessor