I'm extracting the PAC parser from my ongoing work to better support proxies in order to lessen the review burden of the final work. Note that this PR will add an unused function and that's okay.

In order to know what to tell Git (or cURL rather) what (if any) proxy it should be using we'll first need to figure out what the system is set up to use. For that we'll leverage the, poorly documented, resolveProxy method in Electron. The method returns a PAC string which we'll need to parse in order to convert it to something that's usable for cURL which is the entire purpose of this method.

The code is documented (perhaps overly so) with several references that's useful if you've never heard of PAC files or PAC strings. The best primer IMO is MDN's article on PAC files.

We don't have to support all the weird variants or the raw output of an actual FindProxyForURL if a user's organization has one set up since Chromium will do an initial parsing round and reformat before handing it off to us.

TL;DR Chops and mashes some strings with more documentation than logic