no-empty-file: Fix false positive with triple-slash directives

[manovotny]

The simplest fix seems to be to ignore .d.ts files as @babel/eslint-parser and @typescript-eslint/parser still view triple-slash directives as regular comments that produce an empty body.

Fixes #1598

[fisker]

I think it's possible to get all comments and test that it's start with a /.

[manovotny]

@fisker I am trying the "starts with /" route, but shebangs are giving me trouble as they meet that criteria too. I'll keep fiddling.

[fisker]

I 'm not familiar with this syntax, but I see this line https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/src/rules/triple-slash-reference.ts#L96

Maybe we can ignore file, if

1. Starts with / and not one first line, shebang has to be on first line.
2. Starts with /\s*<reference\s*, we can add missing cases later.

[fisker]

Wait, I don't think .d.ts can use shebang, so filename check push first char should enough ?

[manovotny]

@fisker yeah, never mind. I was making it more difficult than it needed to be. PR has been updated.

[fisker]

Good job! Thank you!

[manovotny]

@fisker you're welcome!