enable rule to warn about Buffer constructor usage

[shiftkey]

Overview

As part of testing the rebase flow I kept noticing this warning from within the Dev Tools:

(node:63731) [DEP0005] DeprecationWarning: Buffer() is deprecated due to security and usability issues. Please use the Buffer.alloc(), Buffer.allocUnsafe(), or Buffer.from() methods instead.

This was a warning from our upgrade to Electron 3 (that now uses Node 10) about some API changes in Node core.

Description

Some of the Buffer constructor APIs have been deprecated since Node 10.0 and will likely be removed at a later date:

The reasons why have been outlined in nodejs/node#4660 and a more in-depth writeup in https://github.com/ChALkeR/notes/blob/master/Lets-fix-Buffer-API.md.

It's not something that is keeping me awake at night currently, but seeing it on every launch while I test locally in dev tools has annoyed me enough to address it.

I've enabled the no-buffer-constructor eslint to find anywhere we use this API in the codebase, and I plan to clean these up the violations by swapping them to the recommend APIs.

Release notes

Notes: no-notes

[shiftkey]

I plan to merge this today once the build goes green, to ensure this goes out with the next beta this week.