code: FieldDescriptor getFieldDescriptor(TypeCache.CachedType<?> cachedType, String signature) {
          FieldDescriptor fieldDescriptor = cachedType.getField(signature);
          if (fieldDescriptor == null) {
              fieldDescriptor = scannerContext.getStore().create(FieldDescriptor.class);
              fieldDescriptor.setSignature(signature);
              cachedType.addMember(signature, fieldDescriptor);
          }
          return fieldDescriptor;
      }
docs: Return the field descriptor for the given type and field signature.
  
  @param cachedType
  The containing type.
  @param signature
  The field signature.
  @return The field descriptor.