Expand var-args before passing to KeyGenerator

Update `CacheAspectSupport` to expand any var-arg parameters before
calling `KeyGenerator` implementations. Prior to this commit var-args
would be passed to `KeyGenerator` implementations as a nested array,
often causing the same key to be generated regardless of the arguments.

Issue: SPR-10870

spring-aspects/src/test/java/org/springframework/cache/config/AnnotatedClassCacheableService.java

@@ -87,6 +87,12 @@ public class AnnotatedClassCacheableService implements CacheableService<Object>
 		return counter.getAndIncrement();
 	}
 
+	@Override
+	@Cacheable(value = "default")
+	public Object varArgsKey(Object... args) {
+		return counter.getAndIncrement();
+	}
+
 	@Override
 	@Cacheable(value = "default", key = "#root.methodName + #root.caches[0].name")
 	public Object name(Object arg1) {

spring-aspects/src/test/java/org/springframework/cache/config/CacheableService.java

@@ -44,6 +44,8 @@ public interface CacheableService<T> {
 
 	T key(Object arg1, Object arg2);
 
+	T varArgsKey(Object... args);
+
 	T name(Object arg1);
 
 	T nullValue(Object arg1);

spring-aspects/src/test/java/org/springframework/cache/config/DefaultCacheableService.java

@@ -91,6 +91,12 @@ public class DefaultCacheableService implements CacheableService<Long> {
 		return counter.getAndIncrement();
 	}
 
+	@Override
+	@Cacheable(value = "default")
+	public Long varArgsKey(Object... args) {
+		return counter.getAndIncrement();
+	}
+
 	@Override
 	@Cacheable(value = "default", key = "#root.methodName")
 	public Long name(Object arg1) {