Upgrade to ASM master (including early support for Java 21 bytecode)

Closes gh-29910

spring-core/src/main/java/org/springframework/asm/ClassReader.java

@@ -194,7 +194,7 @@ public class ClassReader {
     this.b = classFileBuffer;
     // Check the class' major_version. This field is after the magic and minor_version fields, which
     // use 4 and 2 bytes respectively.
-    if (checkClassVersion && readShort(classFileOffset + 6) > Opcodes.V20) {
+    if (checkClassVersion && readShort(classFileOffset + 6) > Opcodes.V21) {
       throw new IllegalArgumentException(
           "Unsupported class file major version " + readShort(classFileOffset + 6));
     }

spring-core/src/main/java/org/springframework/asm/Opcodes.java

@@ -285,6 +285,7 @@ public interface Opcodes {
   int V18 = 0 << 16 | 62;
   int V19 = 0 << 16 | 63;
   int V20 = 0 << 16 | 64;
+  int V21 = 0 << 16 | 65;
 
   /**
    * Version flag indicating that the class is using 'preview' features.