Error message mentioning `function$`

[cknitt]

v11 uncurried mode:

let (value, setValue) = React.useState(() => None)

// Correct
setValue(_ => Some(42))

// Incorrect
setValue(Some(42))

Error message for the second setValue:

The constructor Some does not belong to type function$
  
  This variant expression is expected to have type option<int> => option<int>

function$ is an implementation detail of uncurried functions and should not appear in a user-facing error message.

[cknitt]

Fixed in #6694