clean up Array.from in codebase (closes #3109)

[kgeorgiou]

Removed all Array.from usages that were wrapping the results of a document.querySelectorAll.

The only Array.from usage left in the codebase is a legitimate one (converts an HTMLCollection to an array):
https://github.com/mozilla/foundation.mozilla.org/blob/2f2c49a8b8713cc9edcc2dd89ef5cd7abb5e34b3/source/js/main.js#L521-L523

I've also removed some unnecessary length checks before iterating the array returned by document.querySelectorAll. If no matches are returned by the query selector, an empty array is returned. [].forEach() wouldn't do anything so protecting the iteration on the length of the array being greater than 0 is excessive.

Closes #3109

Checklist

Tests

• Is the code I'm adding covered by tests?

[Pomax]

Nice, thank you so much for doing this. If I can ask, how did you decided to work on this issue? (this repo is not on any "good for contributors" lists, and we're a small enough team to usually not ask for contributions because there's not enough spare time for people to walk contributors through the code to the point where they can meaningfully contribute).

[kgeorgiou]

Hey @Pomax, no worries!

I love Mozilla & OSS so I really wanted to start my quest for Hacktorberfest here!

Let me know if there are any other issues I could help with.

[Pomax]

just one change.

[Pomax]

Apologies for the long delay, I've ported your changes over to #4262 and should be able to land that this sprint. Thanks again for helping.

[kgeorgiou]

Apologies for the long delay, I've ported your changes over to #4262 and should be able to land that this sprint. Thanks again for helping.

No worries 🙌 Thanks!