Summary
-------

Represent the `superclass` and `superinterfaces` in `ClassTypeSig` with `ClassTypeSig` and `List<ClassTypeSig>`.

Problem
-------

In JVMS 4.7.9.1, the superclass and superinterfaces of a class signature is required to be class signatures. Yet Class-File API uses a `RefTypeSig`, allowing potentially invalid signatures, like using an array class as a superclass.

Solution
--------

Change the `superclass` and `superinterfaces` in `ClassTypeSig` from `RefTypeSig` and `List<RefTypeSig>` to `ClassTypeSig` and `List<ClassTypeSig>`.

Specification
-------------

    --- a/src/java.base/share/classes/java/lang/classfile/ClassSignature.java
    +++ b/src/java.base/share/classes/java/lang/classfile/ClassSignature.java
    @@ -42,10 +42,10 @@ public sealed interface ClassSignature
         List<Signature.TypeParam> typeParameters();
     
         /** {@return the instantiation of the superclass in this signature} */
    -    Signature.RefTypeSig superclassSignature();
    +    Signature.ClassTypeSig superclassSignature();
     
         /** {@return the instantiation of the interfaces in this signature} */
    -    List<Signature.RefTypeSig> superinterfaceSignatures();
    +    List<Signature.ClassTypeSig> superinterfaceSignatures();
     
         /** {@return the raw signature string} */
         String signatureString();
    @@ -55,8 +55,8 @@ public sealed interface ClassSignature
          * @param superclassSignature the superclass
          * @param superinterfaceSignatures the interfaces
          */
    -    public static ClassSignature of(Signature.RefTypeSig superclassSignature,
    -                                    Signature.RefTypeSig... superinterfaceSignatures) {
    +    public static ClassSignature of(Signature.ClassTypeSig superclassSignature,
    +                                    Signature.ClassTypeSig... superinterfaceSignatures) {
             return of(List.of(), superclassSignature, superinterfaceSignatures);
         }
     
    @@ -67,8 +67,8 @@ public static ClassSignature of(Signature.RefTypeSig superclassSignature,
          * @param superinterfaceSignatures the interfaces
          */
         public static ClassSignature of(List<Signature.TypeParam> typeParameters,
    -                                    Signature.RefTypeSig superclassSignature,
    -                                    Signature.RefTypeSig... superinterfaceSignatures) {
    +                                    Signature.ClassTypeSig superclassSignature,
    +                                    Signature.ClassTypeSig... superinterfaceSignatures) {
             return new SignaturesImpl.ClassSignatureImpl(
                     requireNonNull(typeParameters),
                     requireNonNull(superclassSignature),