ref(lint): Add new eslint rule default-export-function-style

[ryan953]

Implements the rule spec'd in sindresorhus/eslint-plugin-unicorn#1089

We have about 1,000 violations of this check, places where we did:

function MyThing() {...}
export default MyThing;

which could be a few less lines, and more importantly we could have all the important info in the method signature:

export default function MyThing() {...}

so it's added as a 'warn' to start

Totally expecting to hear about named imports. This isn't adding or removing anything as it relates to that topic.

[getsantry]

This pull request has gone three weeks without activity. In another week, I will close it.

But! If you comment or otherwise update it, I will reset the clock, and if you add the label WIP, I will leave it alone unless WIP is removed ... forever!

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"A weed is but an unloved flower." ― Ella Wheeler Wilcox 🥀