Wrongly generated Axios clients when not using dto

[dubzzz]

It seems that the Axios code generated by NSwag when we move from "typeStyle": "Class" to"typeStyle": "Interface" comes with a bug.

This Pull Request is supposed to fix the issue. Please let me know if I can add a specific test to cover this case and avoid it to come back in the future.

---

Here is the behaviour I observed when moving from "typeStyle": "Class" to"typeStyle": "Interface".

Actually here are the codes for process* that have been generated with "typeStyle": "Class":

    // Here we are dealing with a complex class
    // Following snippet was called by:
    /*
        return this.instance.request(options_).catch((_error: any) => {
            if (isAxiosError(_error) && _error.response) {
                return _error.response;
            } else {
                throw _error;
            }
        }).then((_response: AxiosResponse) => {
            return this.processCreateUser(_response);
        });
    */
    protected processCreateUser(response: AxiosResponse): Promise<User> {
        const status = response.status;
        let _headers: any = {};
        if (response.headers && typeof response.headers === "object") {
            for (let k in response.headers) {
                if (response.headers.hasOwnProperty(k)) {
                    _headers[k] = response.headers[k];
                }
            }
        }
        if (status === 201) {
            const _responseText = response.data;
            let result201: any = null;
            let resultData201  = _responseText;
            result201 = User.fromJS(resultData201);
            return result201;
        } else if (status !== 200 && status !== 204) {
            const _responseText = response.data;
            return throwException("An unexpected server error occurred.", status, _responseText, _headers);
        }
        return Promise.resolve<User>(<any>null);
    }

    // Here we are dealing with a simple string
    // Following snippet was called by:
    /*
        return this.instance.request(options_).catch((_error: any) => {
            if (isAxiosError(_error) && _error.response) {
                return _error.response;
            } else {
                throw _error;
            }
        }).then((_response: AxiosResponse) => {
            return this.processNewPassword(_response);
        });
    */
    protected processNewPassword(response: AxiosResponse): Promise<string> {
        const status = response.status;
        let _headers: any = {};
        if (response.headers && typeof response.headers === "object") {
            for (let k in response.headers) {
                if (response.headers.hasOwnProperty(k)) {
                    _headers[k] = response.headers[k];
                }
            }
        }
        if (status === 200) {
            const _responseText = response.data;
            let result200: any = null;
            let resultData200  = _responseText;
            result200 = resultData200 !== undefined ? resultData200 : <any>null;
            return result200;
        } else if (status !== 200 && status !== 204) {
            const _responseText = response.data;
            return throwException("An unexpected server error occurred.", status, _responseText, _headers);
        }
        return Promise.resolve<string>(<any>null);
    }

In this version of process*, response.data holds the output as a normal JS Objects not a raw string that should be parsed to extract something from it. When we toggle "typeStyle": "Interface", the code JSON.parse(response.data) crashes as we try to parse an object (or an already parsed string).

When I moved towards "typeStyle": "Interface":

    // Here we are dealing with a complex class
    // Following snippet was called by:
    /*
        return this.instance.request(options_).catch((_error: any) => {
            if (isAxiosError(_error) && _error.response) {
                return _error.response;
            } else {
                throw _error;
            }
        }).then((_response: AxiosResponse) => {
            return this.processCreateUser(_response);
        });
    */
    protected processCreateUser(response: AxiosResponse): Promise<User> {
        const status = response.status;
        let _headers: any = {};
        if (response.headers && typeof response.headers === "object") {
            for (let k in response.headers) {
                if (response.headers.hasOwnProperty(k)) {
                    _headers[k] = response.headers[k];
                }
            }
        }
        if (status === 201) {
            const _responseText = response.data;
            let result201: any = null;
            let resultData201  = _responseText;
            result201 = JSON.parse(resultData201);
            return result201;
        } else if (status !== 200 && status !== 204) {
            const _responseText = response.data;
            return throwException("An unexpected server error occurred.", status, _responseText, _headers);
        }
        return Promise.resolve<User>(<any>null);
    }

    // Here we are dealing with a simple string
    // Following snippet was called by:
    /*
        return this.instance.request(options_).catch((_error: any) => {
            if (isAxiosError(_error) && _error.response) {
                return _error.response;
            } else {
                throw _error;
            }
        }).then((_response: AxiosResponse) => {
            return this.processNewPassword(_response);
        });
    */
    protected processNewPassword(response: AxiosResponse): Promise<string> {
        const status = response.status;
        let _headers: any = {};
        if (response.headers && typeof response.headers === "object") {
            for (let k in response.headers) {
                if (response.headers.hasOwnProperty(k)) {
                    _headers[k] = response.headers[k];
                }
            }
        }
        if (status === 200) {
            const _responseText = response.data;
            let result200: any = null;
            let resultData200  = _responseText;
            result200 = JSON.parse(resultData200);
            return result200;
        } else if (status !== 200 && status !== 204) {
            const _responseText = response.data;
            return throwException("An unexpected server error occurred.", status, _responseText, _headers);
        }
        return Promise.resolve<string>(<any>null);
    }

[dubzzz]

Closing this PR for the moment, it might already be handled by #2927