Validator - check for required properties in tileset.json about 3d-tiles-validator

[javagl]

This should have been closed via #222 (comment)

Having missing properties (like the missing geometricError) in a tileset like this

{
  "asset" : {
    "version" : "1.1"
  },
  "root" : {
    "boundingVolume" : {
      "box" : [ 0.5, 0.5, 0.5, 0.5, 0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.0, 0.5 ]
    },
    "geometricError" : 1.0
  }
}

will now generate an issue like this

Validation result:
{
  "date": "2022-10-04T15:00:06.894Z",
  "numErrors": 1,
  "numWarnings": 0,
  "issues": [
    {
      "type": "PROPERTY_MISSING",
      "path": "/geometricError",
      "message": "The 'geometricError' property is required",
      "severity": "ERROR"
    }
  ]
}

The same should be the case for all required filelds.