[typescript-axios] reuse fp objects in classes

Created by: stropho

There are several generated entities that can be used to create a request. The commonly used are the generated: class or api factory. Both of these entities use an FP entity internally - let's call it a lower layer used to accomplish a request; we don't need to go deeper than that.

Current behaviour for api factory : FP is created once for all the request (within a single factory product). Example from https://github.com/OpenAPITools/openapi-generator/blob/d8bed4228d8b0aa5e5f0c12b4485d20c7310505c/samples/client/petstore/typescript-axios/builds/default/api.ts#L714

export const PetApiFactory = function (configuration?: Configuration, basePath?: string, axios?: AxiosInstance) {
    const localVarFp = PetApiFp(configuration)
    return {
        /**
         * 
         * @summary Add a new pet to the store
         * @param {Pet} body Pet object that needs to be added to the store
         * @param {*} [options] Override http request option.
         * @throws {RequiredError}
         */
        addPet(body: Pet, options?: any): AxiosPromise<void> {
            return localVarFp.addPet(body, options).then((request) => request(axios, basePath));
        },
}

Current behaviour for a class: FP is created for every request. Example from https://github.com/OpenAPITools/openapi-generator/blob/d8bed4228d8b0aa5e5f0c12b4485d20c7310505c/samples/client/petstore/typescript-axios/builds/default/api.ts#L821

export class PetApi extends BaseAPI {
    /**
     * 
     * @summary Add a new pet to the store
     * @param {Pet} body Pet object that needs to be added to the store
     * @param {*} [options] Override http request option.
     * @throws {RequiredError}
     * @memberof PetApi
     */
    public addPet(body: Pet, options?: AxiosRequestConfig) {
        return PetApiFp(this.configuration).addPet(body, options).then((request) => request(this.axios, this.basePath));
    }
}

This PR enforces the objects (class instances) to use a signle FP entity.

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
• Run the following to build the project and update samples:

  ./mvnw clean package 
  ./bin/generate-samples.sh
  ./bin/utils/export_docs_generators.sh

  Commit all changed files. This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master. These must match the expectations made by your contribution. You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/configs/java*. For Windows users, please run the script in Git BASH.
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