fix parenthesis matching for JSON validation.

[alfy91]

Issue description

In the JSON validator, there is a bug that occurs only for the closing parenthesis. For example, this JSON resource

{
  "resourceType": "Bundle",
  "type": "collection",
  "entry": [
    {
      "fullUrl": "urn:uuid:550e8400-e29b-41d4-a716-446655440000",
      "resource": {
        "resourceType": "Patient",
        "id": "550e8400-e29b-41d4-a716-446655440000",
        "name": [
          {
            "use": "official",
            "family": "Robin",
            "given": ["Christopher"]
          ] /*<------- wrong parenthesis*/
        ]
      }
    }
  ]
}

Is considered correct from the validator, but in reality there is a wrong parenthesis ('}' is the correct one). This issue happens with any kind of special character, so also this JSON is considered correct by the validator:

{
  "resourceType": "Bundle",
  "type": "collection",
  "entry": [
    {
      "fullUrl": "urn:uuid:550e8400-e29b-41d4-a716-446655440000",
      "resource": {
        "resourceType": "Patient",
        "id": "550e8400-e29b-41d4-a716-446655440000",
        "name": [
          {
            "use": "official",
            "family": "Robin",
            "given": ["Christopher"]
          # /*<------- wrong char*/
        ]
      }
    }
  ]
}

Proposed Solution

I added, in the JSONLexer, a check for the parenthesis matching. Through a stack, the parenthesis matching is checked, and the relative error is given.

This commit alfy91@29484b2
contains the details of the solution.

[grahamegrieve]

did you make any test cases?