fix unique names inside (-) functions in core parsing

[TimWhiting]

fun (-)(l1: list<a>, l2: list<a>, ?(==): (a, a) -> e bool): e list<a>
  l1.filter(fn(x) !l2.any(fn(y) y == x))

fun main()
  [1, 2, 3] - [3, 4, 5]

Monadic lifting creates a unique name based on the top level identifier

// core identifier
fun @mlift-x-@10007[1,0,1,0] : forall<(e :: E)> (@y-x10004 : std/core/types/bool) -> (e :: E) std/core/types/bool;

However, @ is not a valid follow character after -

We could change unique names, or change lexing to allow this as an identifier. I chose the latter in this PR.

Also, the implicits translation / open effects can add let identifiers such as the following below:

fun @lift-handle-cache@10567 // inline size: 3
  = tp... {
    val @implicit/(@uniq-x@10158==)[

I edited Core/Parse.hs to allow locally qualified identifiers inside function definitions.

[daanx]

Thanks TIm!