Test the ApplicationContextAotGenerator with the agent

This commit adds new tests for the `ApplicationContextAotGenerator`,
this time leveraging the `RuntimeHintsAgent` that checks the need for
runtime hints at runtime.

See gh-27981

spring-context/spring-context.gradle

@@ -1,3 +1,7 @@
+plugins {
+	id 'org.springframework.build.runtimehints-agent'
+}
+
 description = "Spring Context"
 
 apply plugin: "kotlin"