fix: various automagic npm module installation fixes

[erickzhao]

This PR has 3 bugfixes relating to the way we import npm modules. Each is in a separate commit.

• 5e3a588 Fixes commented npm modules not ignored if comments are multi-line #509 by using the decomment module inside a Web Worker thread.
• 57aa3d1 Fixes npm modules installing multiple times if required in multiple editors #510 by adding the list of modules detected into a Set().
• 7ebbeac Fixes npm modules don't load on preload editor #511 by adding preload to the list of editors that we check modules for.
• 93c24dd adds tests to make sure everything works. :)

Note: this PR adds in a new dependency to the decomment module, which uses the Esprima JavaScript parser under the hood to strip any JS code fed in of its comments. I decided to use a library rather than play around with regexes for reliability's sake. decomment is licensed under MIT, so it should be compatible with Electron Fiddle for licensing purposes.

[coveralls]

Coverage decreased (-0.05%) to 93.545% when pulling 93c24dd on erick/npm-polishing into df22a5f on master.

[felixrieseberg]

Big fan, but I'm pretty unsure about including decomment, which bundles esprima. That's ten Reacts in terms of size 😬

[erickzhao]

@felixrieseberg I agree that it's a pretty big package to fix an edge case in our code, but if we want to provide a stable experience for users to require packages automatically, using a parser rather than regex to detect these module installs should be the way to go, even if it's to solve an edge case.

Are there big performance impacts at this bundle level for loading the local bundle? For reference, decomment seems to be 135kb minified while react-dom is 121kb.

As for alternatives, I'm not too familiar with using different parsers, but we could probably shave off 25kb here by using acorn or meriyah directly instead. I'm not sure we can decrease that any further.

Maybe we can lazy load the module rather than import at the top of the file?

[issacgerges]

Its unfortunate you can't lean on the tokenizer that's being used internally by monaco. I played around with this a bit but wasn't able to get access to it. microsoft/monaco-typescript#65

I think the only real impact of bloat here is a small bump in bundle size and load time spent parsing/optimizing the additional javascript.

[felixrieseberg]

Good stuff! I'd only check whether this survives compilation but it looks fantastic otherwise 👏