Exporting Param classes to allow their import from firebase-functions/params

[cborac]

Description

Exported Param classes: BooleanParam, FloatParam, IntParam, SecretParam, StringParam, and ListParam.

Upon creating stubs using various tools to test my cloud functions which use firebase-functions, I faced an issue where I could not mock defineSecret as it was called too early. I could stub it before importing the function file, but it would impair the coding conventions, and cause more effort.

As a result, I tried to import SecretParam and tried to stub its prototype. Upon running, I had an error Package subpath './lib/params/types' is not defined by "exports" which is reasonable as it is not exported by default and rather used as a local class.

Despite presumably being a DX choice (to avoid wrongfully creating params), it causes trouble and limits the users' ability to interact with the library.

This PR doesn't break any existing code.

Code sample

Here's an example in TypeScript of creating a stub with the sinon library

import { params } from "firebase-functions";
import * as sinon from "sinon";

const fakeSecrets = {
     "secret1":  "secr3t.value"
};

sinon.stub(params.SecretParam.prototype, "value").callsFake(function (this: params.SecretParam) {
     return fakeSecrets[this.name];
});


const secret = defineSecret("secret1");
console.log(secret.value());   // "secr3t.value"

[cborac]

Also, to avoid confusion, the example I have given can be replaced by setting the proper process.env. However, the issue still persists in other circumstances.

https://github.com/firebase/firebase-functions/blob/a70663b0c6d2da08b665951686ef5bc35ebc0167/src/params/types.ts#L381C17-L381C24