Custom coded scalars not working as mutation input

[Ryan Billard]

Not sure when this broke, but custom coded scalars are not encoded properly if they are a direct input to a mutation in Swift.

Operation.stencil is actually looking for a requiresCustomEncoder flag here, but we never actually pass that in from the Renderer.

We probably just need to use the same logic used to determine the requiresCustomEncoder flag that the renderer for input types uses here.

sample GraphQL mutation that fails.

mutation CreateGiftCard($initialValue: Decimal!, $code: String, $customerId: ID, $expiresOn: Date, $note: String, $templateSuffix: String) {
  giftCardIssue(initialValue: $initialValue, code: $code, customerId: $customerId, expiresOn: $expiresOn, note: $note, templateSuffix: $templateSuffix) {
    userErrors {
      message
      field
    }
  }
}