Refactor Script query to use IScript property

[russcam]

The current ScriptQuery implementation includes separate properties at the root level for properties of a script:

elasticsearch-net/src/Nest/QueryDsl/Specialized/Script/ScriptQuery.cs

Lines 8 to 28 in 9f3e657

	[JsonConverter(typeof(ScriptQueryConverter))]
	[JsonObject(MemberSerialization = MemberSerialization.OptIn)]
	public interface IScriptQuery : IQuery
	{
	[JsonProperty("id")]
	Id Id { get; set; }
	[Obsolete("Use Source. Inline is deprecated and scheduled to be removed in Elasticsearch 7.0")]
	[JsonIgnore]
	string Inline { get; set; }
	[JsonProperty("lang")]
	string Lang { get; set; }
	[JsonProperty("params")]
	[JsonConverter(typeof(VerbatimDictionaryKeysJsonConverter<string, object>))]
	Dictionary<string, object> Params { get; set; }
	[JsonProperty("source")]
	string Source { get; set; }
	}

This results in the need to have a custom JsonConverter/serialization component in order to correctly nest these properties in JSON:

{
  "script": {
    "_name": "named_query",
    "boost": 1.1,
    "script": {
      "source": "doc['numberOfCommits'].value > param1",
      "params": {
        "param1": 50
      }
    }
  }
}

These properties should be removed and replaced with an IScript Script {get;set;} property

[russcam]

This is now merged into 7.x in 153bbf3