support early returns and typeof checks for feature detection

[bschlenk]

Hey Amila, thanks for building this plugin!

Sorry for the large PR, I'm hoping this will spark some discussion mainly, the code here is still WIP. But I wanted to get it in front of you before I get too far along.

As a lot of the issues point out, if statements prevent this plugin from detecting browser compat issues, and I wanted to take a shot at fixing it. But I wound up taking a few steps more and fixed a few other things.

Fundamentally this sort of changes how this plugin is implemented. But I think it makes sense as far as what this plugin is meant to catch. When I think about these apis, I don't really care whether they're function calls, new statements, or member expressions. The error is simply that the object/method doesn't exist in certain browsers, and that's what we want to catch.

With that in mind, this PR changes the approach to only lint on Identifier nodes. And it focuses on what types of operations would cause runtime errors. So any code that is testing if a feature exists is now okay:

if (window.fetch) {
  fetch()
}

if (!window.fetch) return;
fetch()

if (typeof fetch === "undefined") return;
fetch()

if (typeof fetch === "function") {
  fetch()
}

But if you do something that would result in a ReferenceError, we'll report it:

// this would throw a ReferenceError so it gets reported
if (fetch) {
  fetch()
}

I did a bit of other cleanup too, if that's desirable:

• remove unnecessary types that TypeScript can infer automatically
• use the types from eslint rather than redefining them
• fixed the sorting of browser targets so they print out in alphabetical order, instead of reverse order

I'm happy to make whatever changes you'd like! I very much want to use this plugin, and these issues were the main blockers for me. I also plan on adding linting for unsupported regex features, and probably going through the list of other issues as well.

fixes:

• why inside If statement is exempt #545
• Feature detection does not respect return statements #523
• Consider typeof in feature detection #520
• Not working IF sentence inside #428
• Feature detection change stops all compat linting of the content of any if statements  #404