Compile-time constant check allows interpolated strings

[jeskew]

Bicep version
0.19.5

Describe the bug
The compile-time constant visitor raises no errors if it encounters an interpolated string, even though this would be compiled to an expression in the JSON template.

To Reproduce

The following Bicep template will produce the following compiled JSON template:

@description('foo${'bar'}')
param baz int

{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "metadata": {
    "_generator": {
      "name": "bicep",
      "version": "0.19.5.34762",
      "templateHash": "17031902422687725027"
    }
  },
  "parameters": {
    "baz": {
      "type": "int",
      "metadata": {
        "description": "[format('foo{0}', 'bar')]"
      }
    }
  },
  "resources": []
}