[bs-73] Tweak algorithm for detecting anonymous classes

Apparently an anonymous class in Groovy is no anonymous in the compiled code,
so we need another heuristic.  We now check for non-existence of public
constructors (if there are none then there's no point regsistering that
class with an application context).

[#48718891]

spring-bootstrap/src/main/java/org/springframework/bootstrap/BeanDefinitionLoader.java

@@ -156,7 +156,8 @@ class BeanDefinitionLoader {
 	private boolean isComponent(Class<?> type) {
 		// Nested anonymous classes are not eligible for registration, nor are groovy
 		// closures
-		if (type.isAnonymousClass() || type.getName().contains("$_closure")) {
+		if (type.isAnonymousClass() || type.getName().contains("$_closure")
+				|| type.getConstructors() == null || type.getConstructors().length == 0) {
 			return false;
 		}
 		return true;