Resolve response type name conflict in angular typescript lib

Created by: grking8

Rename variable so it does not clash with responseType parameter which is required for OAuth2 - fixes https://github.com/OpenAPITools/openapi-generator/issues/5853

2nd attempt: I checked samples/client/petstore/typescript-angular-v11-provided-in-root/builds/with-npm/api/pet.service.ts

        return this.httpClient.post<any>(`${this.configuration.basePath}/pet`,
            body,
            {
                responseType: <any>responseType_,
                withCredentials: this.configuration.withCredentials,
                headers: headers,
                observe: observe,
                reportProgress: reportProgress
            }
        );

CC @TiFu (2017/07) @taxpon (2017/07) @sebastianhaas (2017/07) @kenisteward (2017/07) @Vrolijkx (2017/09) @macjohnny (2018/01) @topce (2018/10) @akehir (2019/07) @petejohansonxo (2019/11) @amakhrov (2020/02)

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