Use Neutrino's extensions in the rest of packages

[helfi92]

No description provided.

[eliperelman]

I grepped the following usages of "extensions":

packages/eslint/index.js:            extensions: ['js', 'jsx'],
packages/jest/src/index.js:    ...neutrino.config.resolve.extensions.values().map(e => e.replace('.', ''))

[helfi92]

Webstorm didn't do a good job at grepping. @eliperelman I started using ag for searching files. Amazing tool. It ignores everything listed in .gitignore which is pretty neat.

[eliperelman]

The current changes are good, but I also noticed when trying to rebase my create-project PR that I needed to update the calls to .test() for some items.

Grep for all the usages of .test() and see if they need to be replaced with something like:

.test(options.test || neutrino.regexFromExtensions())

[eliperelman]

[edmorley]

This means eslint will now be run against .json files too. Is this intended? (For example if people have the "enforce trailing commas" eslint rule enabled, eslint will complain unless the .json is changed to be invalid)

[eliperelman]

Have we tested that this really happens? That would be weird! It would also mean single quote properties and values would also break...I guess we should find out. If it does, we can filter json from the list. Good catch.