Imported variables into .bicepparam from ARM JSON templates are not evaluated

[jeskew]

Bicep version
0.26.170

Describe the bug
Ran into this while working on #13997. When importing from ARM JSON templates into .bicepparam files, expressions in variable declarations will not be evaluated. I believe this is a regression introduced in version 0.25.53, so importing from JSON into .bicepparam files must be used infrequently (if at all).

To Reproduce
main.bicep

param intParam int

test.json

{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "metadata": {
    "_generator": {
      "name": "bicep",
      "version": "0.26.170.59819",
      "templateHash": "15627574382354327639"
    },
    "__bicep_exported_variables!": [
      {
        "name": "a"
      }
    ]
  },
  "variables": {
    "a": "[add(2, 2)]"
  },
  "resources": []
}

test.bicepparam

using 'main.bicep'

import { a } from 'test.json'

param intParam = a

Compiling test.bicepparam will result in the following JSON:

{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentParameters.json#",
  "contentVersion": "1.0.0.0",
  "parameters": {
    "intParam": {
      "value": "[add(2, 2)]"
    }
  }
}