Fix: Allow escaped whitespace in paths for config initialization (fixes #11099)

[getify]

What is the purpose of this pull request?

[x] Bug fix

Reproduced and fixed issue #11099 with:

ESLint Version: v5.9.0
Node Version: v10.4.1

What changes did you make?

I changed the regex used in splitting the paths, to skip splitting on an escaped space. Then I remove any leftover \ characters from the split-out patterns using a .map(..).

Is there anything you'd like reviewers to focus on?

Because I'm using a regex negative lookbehind, it means this config tool could only run in Node with that recent JS feature present (ES2018), which (I think) was Node 10.0+. Not sure how that impacts eslint's Node support.

Also, I was going to modify the tests for config-initializer here, but decided not to, because it's not clear if there's any reasonable way to get an internal path in eslint with a space in it to be able to test against. :/

[jsf-clabot]

All committers have signed the CLA.

[not-an-aardvark]

Thanks for the PR!

Re. regex negative lookbehind, ESLint still needs to support Node 6 (see here for the precise supported versions), so I don't think we can use negative lookbehinds yet. Could this be refactored to avoid negative lookbehinds?

For the config-initializer tests, would it work to create a folder with a space within tests/fixtures (e.g. tests/fixtures/folder name with a space/myFile.js) and use files in that folder for the test?

[platinumazure]

Could you please add some tests? Thanks!

Also, is negative lookbehind supported in all versions of Node that ESLint supports?