Include fs-extra methods

[aminya]

Description of the change

This adds fs-extra methods. In the export section of the library, they are considered "after" fs-plus methods, so it will not have any conflict or breakage.

Future Improvements

The method that this PR adds fs-extra is minimal. Later, I will add support for named exports and tree-shaking.

Currently, there are a few methods that are used in both packages. Technically, we do not need to use mkdirp, rimraf, etc anymore since fs-extra supports all of these (with a more up to date implementation). Some other methods from the fs-plus are not using the native fs functions which means they do not support all types of inputs such as Buffer or URL. In future PRs, I will write a few type-dispatch sentences to decide between the native implementation and fs-plus implementation. This allows keeping the methods of fs-plus that offer anything interesting over the native fs functions.

copyFileSync
existsSync
writeFile
writeFileSync
copySync
copy
moveSync
move
remove
removeSync

So, this PR paves the way for future PRs. 🚀

Benefits

fs-extra has many good methods which we can use. We will not need to install two separate fs library anymore! Including fs-extra in the Atom snapshot means that anyone using fs-extra will benefit from the speed up! 🎉

Verification

All the tests pass.

Release Notes

• Include fs-extra methods in fs-plus.

[jimmywarting]

node have built in support for mkdirp and rimraf now... neither you or fs.extra need to provide this methods

[aminya]

@jimmywarting This package is used inside Electron, which still uses Node 12. The functions you mentioned are either non-available or are not backward compatible with the users of this library (require manual updating).