This question looks dated and the feature for creating http API GW v2 via OpenAPI specs (as replacement for API GW V1 REST API) is now supported.

See: https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/apigatewayv2_api#body-1

There is an interesting module here that has such functionality to get started with. : https://github.com/terraform-aws-modules/terraform-aws-apigateway-v2