Refactor and update index.js to use fdir()

[queengooborg]

This PR updates index.js in a couple of ways:

1. Replaces the use of the arguments keyword with a defined ...files argument (for both consistency and function legibility)
2. Adds a comment to indicate this file is a part of BCD
3. Updates the JSDoc comments
4. Utilizes fdir() to walk the file tree

[ddbeck]

A couple questions on this one

1. Turns the `load()` function into one using arrow syntax

Why?

3. Adds the CC0 copyright notice

Do you know where this text originated? I've started to see it on some scripts, but I have no idea where this text comes from originally. It's… off in some ways and I'm not sure whether we should be reproducing it.

[ExE-Boss]

3. Adds the CC0 copyright notice

Do you know where this text originated? I've started to see it on some scripts, but I have no idea where this text comes from originally. It's… off in some ways and I'm not sure whether we should be reproducing it.

It matches what’s in: https://www.mozilla.org/MPL/headers/#pd-c.

There’s also:

browser-compat-data/LICENSE

Line 1 in f4737ee

CC0 1.0 Universal

[queengooborg]

For the arrow function syntax, we’ve got a lot of functions in our code that use the arrow function syntax. I figured it makes sense to maintain function style consistency! The primary part is the inclusion of the “files” argument, however — when I first saw the function, I was quite confused about how it functioned since I didn’t see the code down below that uses the “arguments” keyword. None of the other loading functions throughout BCD use it; they all have the same “files” argument.

As for the copyright notice, this is because BCD as a whole is licensed under the CC0 license!

[caugner]

LGTM, but unless I'm mistaken the main change of this PR is to migrate to fdir() (from fs.readdirSync()), and this should be mirrored at least in the PR title (which is used for the squash merge commit), but ideally also in the PR description.

[github-actions]

This pull request has merge conflicts that must be resolved before we can merge this.

[queengooborg]

Uh oh... @foolip this apparently broke the collector because fdir is not crawling relative to the root of index.js. Sending in a fix now.