[C++] HasVariadicBuffers should respect extension types #54924

Describe the bug, including details regarding any error messages, version, and platform.

The current implementation of bool ArraySpan::HasVariadicBuffers does not handle extension types properly and always reports false.

::SetMembers however does handle these explicitly and we should handle extension types in the HasVariadicBuffers implementation similarly:

Type::type type_id = this->type->id();
  if (type_id == Type::EXTENSION) {
    auto* ext_type = checked_cast<const ExtensionType*>(this->type);
    type_id = ext_type->storage_type()->id();
  }

Component(s)

C++