Provide ConfigurationClass#toString implementation

For ease during debugging; prompted while fixing SPR-8761.

org.springframework.context/src/main/java/org/springframework/context/annotation/ConfigurationClass.java

@@ -151,6 +151,11 @@ final class ConfigurationClass {
 		return getMetadata().getClassName().hashCode();
 	}
 
+	@Override
+	public String toString() {
+		return String.format("[ConfigurationClass:beanName=%s,resource=%s]", this.beanName, this.resource);
+	}
+
 
 	/**
 	 * Configuration classes must be non-final to accommodate CGLIB subclassing.