[REQ][typescript] Support x-enum-varnames field

Is your feature request related to a problem? Please describe.

The typescript openapi generator does not seem to support the x-enum-varnames field:

{
  "openapi": "3.0.1",
  "info": {
    "title": "test",
    "description": "test",
    "version": "v1"
  },
  "servers": [
    {
      "url": "",
      "description": "Relative mount"
    },
    {
      "url": "",
      "description": "Production"
    }
  ],
  "paths": {},
  "components": {
    "schemas": {
      "OperationStatus": {
        "enum": [
          0,
          1,
          2,
          3,
          4
        ],
        "x-enum-varnames": [
          "Pending",
          "InProgress",
          "Completed",
          "Failed",
          "Canceled"
        ],
        "type": "integer",
        "format": "int32"
      }
    }
  }
}

Here OperationStatus has a typescript type of just "0" | "1" | "2" | "3" | "4".

Describe the solution you'd like

When x-enum-varnames appears, the type is declared as a named enum.

Start by locating the TypeScript OpenAPI generator's enum-generation entry point and its current handling of x-enum-varnames. Trace any existing enum tests, then confirm that schemas with this field generate a named enum while existing enum generation remains unchanged.