constant_identifier_names false positive for destructured field names

[pq]

Follow-up from #59121.

We should see no lints here.

class A {
  var a_b;
}

f(A a) {
  switch (a) {
    case A(:var a_b):
  }
  switch (a) {
    case A(:var a_b?):
    case A(:var a_b!): 
  }
}