Refactor: convert all functions to arrow functions

[queengooborg]

This PR is a subset of #5654 and #5655 (and partially #5252 (comment)). This PR converts all functions from the older function foo(arg, bar) {} syntax to the const foo = (arg, bar) => {} syntax like most of the functions throughout BCD's scripts.

[ddbeck]

this moves all functions to the top level for code quality purposes

This needs to be at least a separate commit, if not a separate PR. function and => have different semantics, so it's potentially two material changes, if the move happens at the same time. That'll be hard to review otherwise.

Please forgive me for being a broken record on this sort of thing. 😄

[ddbeck]

Hi Vinyl, thank you for opening this PR, but I'm going to close it. I'm not really happy about it, but I think it's hard to do otherwise. I think the spirit and effect of these changes are probably good in isolation, but as a big PR that touches so many files for what's substantially a style concern, it feels both risky and difficult to review.

However, I do recognize that this inches us toward #5252. My take on ESLint is that I would still like to start applying its recommendations to our code base, but I think we'll have to do it in really tiny, tiny steps (e.g., going file by file, or maybe even error by error).

Thanks for your understanding on this! 🙏