Support ResolvableTypeProvider on simple event pojo

Previously, the generic type of a simple pojo event implementing
ResolvableTypeProvider wasn't detected properly. This commit fixes the
logic when the generic type is not provided to reuse what
PayloadApplicationEvent is already doing anyway.

Issue: SPR-14029

spring-context/src/main/java/org/springframework/context/support/AbstractApplicationContext.java

@@ -369,7 +369,7 @@ public abstract class AbstractApplicationContext extends DefaultResourceLoader
 		else {
 			applicationEvent = new PayloadApplicationEvent<Object>(this, event);
 			if (eventType == null) {
-				eventType = ResolvableType.forClassWithGenerics(PayloadApplicationEvent.class, event.getClass());
+				eventType = ((PayloadApplicationEvent)applicationEvent).getResolvableType();
 			}
 		}