[BUG] Dashed (-) are transformed to underscores (_)

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• What's the version of OpenAPI Generator used?
• Have you search for related issues/PRs?
• What's the actual output vs expected output?
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Description

I am using openapi-generator with typescript-fetch plugin:

openapi-generator generate -g typescript-fetch --additional-properties=supportsES6=true,typescriptThreePlus=true,modelPropertyNaming=original -o ./open-api -i ./apigateway.json

for some reason, the generator alsways transforms properties adv_1-1 to adv_1_1. meaning, it removes the original -.

spec:

"prices": {
            "type": "object",
            "properties": {
              "adv_1-1": {
                "type": "number"
              },
              "adv_1-2": {
                "type": "number"
              },
              "adv_1-3": {
                "type": "number"
              },
              "adv_1-4": {
                "type": "number"
              },
              "adv_1-6": {
                "type": "number"
              },
              "adv_2-1": {
                "type": "number"
              },
              "adv_2-3": {
                "type": "number"
              },
              "migrateId": {
                "type": "number"
              },
              "mm": {
                "type": "number"
              }
            }
          }

result:

export interface MediaPrintPrices {
    /**
     *
     * @type {number}
     * @memberof MediaPrintPrices
     */
    adv_1_1?: number;
    /**
     *
     * @type {number}
     * @memberof MediaPrintPrices
     */
    adv_1_2?: number;
    /**
     *
     * @type {number}
     * @memberof MediaPrintPrices
     */
    adv_1_3?: number;
    /**
     *
     * @type {number}
     * @memberof MediaPrintPrices
     */
    adv_1_4?: number;
    /**
     *
     * @type {number}
     * @memberof MediaPrintPrices
     */
    adv_1_6?: number;
    /**
     *
     * @type {number}
     * @memberof MediaPrintPrices
     */
    adv_2_1?: number;
    /**
     *
     * @type {number}
     * @memberof MediaPrintPrices
     */
    adv_2_3?: number;
    /**
     *
     * @type {number}
     * @memberof MediaPrintPrices
     */
    migrateId?: number;
    /**
     *
     * @type {number}
     * @memberof MediaPrintPrices
     */
    mm?: number;
}

openapi-generator version

4.1.2

OpenAPI declaration file content or url

Command line used for generation

openapi-generator generate -g typescript-fetch --additional-properties=supportsES6=true,typescriptThreePlus=true,modelPropertyNaming=original -o ./open-api -i ./apigateway.json

Start with the typescript-fetch generator using the command and OpenAPI properties shown in the issue, especially modelPropertyNaming=original. Compare generated property names containing hyphens with the specification, then verify that the generated TypeScript interface preserves those names without changing unrelated properties.