Avoid char array creation in AbstractAspectJAdvice.isVariableName()

See gh-26100

spring-aop/src/main/java/org/springframework/aop/aspectj/AbstractAspectJAdvice.java

@@ -354,8 +354,8 @@ public abstract class AbstractAspectJAdvice implements Advice, AspectJPrecedence
 		if (!Character.isJavaIdentifierStart(name.charAt(0))) {
 			return false;
 		}
-		for (char ch: name.toCharArray()) {
-			if (!Character.isJavaIdentifierPart(ch)) {
+		for (int i = 1; i < name.length(); i++) {
+			if (!Character.isJavaIdentifierPart(name.charAt(i))) {
 				return false;
 			}
 		}