LoadTextContent should take only compile-time constants as parameters

[miqm]

Repro for triage:

works:

var stringArray = [
  './policies/policy_1.json'
]
  
var policies = [for i in range(0, length(stringArray)): json(loadTextContent(stringArray[i]))]

doesn't work:

var stringArray = [
  './policies/policy_1.json'
  './policies/policy_2.json'
]
  
var policies = [for i in range(0, length(stringArray)): json(loadTextContent(stringArray[i]))]

Originally posted by @alex-frankel in #3816 (comment)