RequestValidator shouldn't require (or even expect) a restApi property.

[richardhboyd]

Specifying a requestModel in the MethodOptions of an AddMethod() operations should create the RequestValidator for me. Currently I have to also manually construct a RequestValidator.

Currently I have to build something like this:

    languageResource.addMethod("POST", new apigw.Integration({
      type: apigw.IntegrationType.AWS,
      uri: `arn:aws:apigateway:${cdk.Aws.REGION}:events:path//`,
      integrationHttpMethod: "POST",
      options: options,
    }),
    {
      methodResponses: [{
          statusCode: "200"
        }],
      requestModels: {"application/json": model.getModel(this, myRestAPI) },
      requestValidator: new apigw.RequestValidator(this, "myValidator", {
        restApi: myRestAPI,
        validateRequestBody: true
      })
    })

The validator is being added to a resource, which is inherently attached to a RestAPI. Asking users to specify it again adds no value and we should just add it for them.

[nija-at]

The change will involve deprecating this property in favour of a new property (like reqValidator) of the type RequestValidatorOptions