Require type annotations for builtins

[jjcnn]

We currently use the argument types for builtins to determine which version of the builtin we want to invoke:

let x = Uint128 0
let y = Uint128 1
let z = builtin add x y   (* add : forall 'A. 'A -> 'A -> 'A. 'A is inferred to be Uint128 in this case. *) 

This is inconsistent with the rest of Scilla, where we require explicit type arguments for polymorphic types:

let x = Uint128 0
let y = Uint128 1
let my_add = tfun 'A => fun (x : 'A) => fun (y : 'A) => x
let z = let f = @my_add Uint128 in f x y

Now that we have added type arguments to builtins, it makes more sense to require type arguments for polymorphic builtins:

let x = Uint128 0
let y = Uint128 1
let z1 = builtin add {Uint128} x y    (* Legal *)
let z2 = builtin add {Uint32} x y     (* Illegal : value arguments do not correspond to the type argument *)
let z3 = builtin add x y             (* No longer legal : type argument required *)

See also #598.