ELM parser for negation is implemented incorrectly

[ewoutkramer]

When an expression contains the unary '-', our current parser only accepts literals and quantities and uses string concatenation and multiplication to execute the negation. However, negation is not limited to literals as the following is valid CQL:

library BareMinimum version '0.0.1'
    
using FHIR version '4.0.1'

include cq_core.FHIRHelpers version '4.0.1' called FHIRHelpers

context Patient

define x: 4

define y: -"x"

define z: -5

define q: 4 'kg'

define m: -"q"

The ELM tree should simply use the Negate ELM node instead, and accept any expression with the correct type. See https://cql.hl7.org/04-logicalspecification.html#negate