Migrate "Failing" test cases to regular tests

This commit replaces the use of EngineTestKit to test scenarios where
bean override could not process the test class. There is no need to
run an actual test for this as:

1. Regular integration tests are already validating that adding the
annotation triggers the processing as part of executing the test.
2. The entry point is a ContextCustomizer that can easily be invoked
in a regular test.

As part of harmonizing this, AbstractTestBeanIntegrationTestCase can
be nested, and BeanOverrideTestSuite serve no purpose. The tests can
be executed in an IDE without any special setup.

spring-test/src/test/java/org/springframework/test/context/bean/override/BeanOverrideContextCustomizerTestUtils.java

@@ -18,8 +18,12 @@
 
 import java.util.Collections;
 
+import org.springframework.context.ConfigurableApplicationContext;
 import org.springframework.lang.Nullable;
 import org.springframework.test.context.ContextCustomizer;
+import org.springframework.test.context.MergedContextConfiguration;
+
+import static org.mockito.Mockito.mock;
 
 /**
  * Test utilities for {@link BeanOverrideContextCustomizer} that are public so
@@ -44,4 +48,17 @@ public static ContextCustomizer createContextCustomizer(Class<?> testClass) {
 		return factory.createContextCustomizer(testClass, Collections.emptyList());
 	}
 
+	/**
+	 * Configure the given {@linkplain ConfigurableApplicationContext application
+	 * context} for the given {@code testClass}.
+	 * @param testClass the test to process
+	 * @param context the context to configure
+	 */
+	public static void configureApplicationContext(Class<?> testClass, ConfigurableApplicationContext context) {
+		ContextCustomizer contextCustomizer = createContextCustomizer(testClass);
+		if (contextCustomizer != null) {
+			contextCustomizer.customizeContext(context, mock(MergedContextConfiguration.class));
+		}
+	}
+
 }