GADT record syntax does not accept linearity annotations

In #19928 (closed) @int-index dropped the parser's support for GADT record syntax with multiplicity annotations, since the annotations were not respected. For instance:

{-# LANGUAGE UnicodeSyntax, LinearTypes #-}

module M where

data R where
  D1 :: { d1 :: Int, d1' :: Int } %1 -> R
  DUr :: { dur :: Int, dur' :: Int } -> R

Is rejected with a parser error.

However, I was writing a program in which I made use of the syntax as in D1, expecting to make both d1 and d1' linear fields. On the other hand, I would expect dur and dur' to be an unrestricted field. I suppose I'm treading on undefined behaviour, but I think it is intuitive for linearity annotations to work in this way for GADT record syntax.

Discussion welcome!