Introduce MergedAnnotation finder methods

[philwebb]

Code to locate methods on classes based on annotations currently mostly uses a combination of MethodIntrospector and AnnotatedElementUtils.

For example, in EventListenerMethodProcessor:

spring-framework/spring-context/src/main/java/org/springframework/context/event/EventListenerMethodProcessor.java

Lines 148 to 150 in 6266370

	annotatedMethods = MethodIntrospector.selectMethods(targetType,
	(MethodIntrospector.MetadataLookup<EventListener>) method ->
	AnnotatedElementUtils.findMergedAnnotation(method, EventListener.class));

With the addition of the new MergedAnnotations API along with the annotation index work it might be nicer if we had a first class way to find such methods.

One possible solution would be to add finder methods to MergedAnnotation.

For example:

MergedAnnotation.find(SomeAnnotation.class).onMethodsIn(SomeCandidate.class);

[sbrannen]

Team Decision: features like MethodIntrospector and MergedAnnotations are orthogonal concerns and should therefore not be combined in a common API/implementation.