Upgrade @wordpress/scripts and add ESLint support for ESNext code

[gziolo]

Closes #49.

This PR adds global support for @wordpress/scripts in the project. This allows simplifying the setup of individual blocks which had to use it in the past making the whole project setup much simpler. Instead of having to run npm install in 4 packages which use ESNext, we can now do it once in the root folder and run npm run build to rule them all.

In addition, this PR adds ESLint support for ESNext based packages. We could enable it for other blocks which are ES5 based but we would need to upgrade ESLint to v6 which supports overrides fro extends feature from the config file. I will figure out how to do it in @wordpress/scripts and update here once published to npm.

I also opened a follow-up PR WordPress/gutenberg#16904 so you don't have to silence ESLint error when using wp global.

[mkaz]

Looks good, built and tested each of the blocks. Thanks for updating!
Glad to see the input/output parameters now available for wp scripts

[ntwb]

Per this weeks #core-js chat this week can we follow up the changes discussed please.

Primarily the changes requested are to not remove package.json files from each of the examples, this is so that developers can copy and paste an entire example folder to their and do not have to worry about trying to cheery pick npm commands from the root of the project.

[gziolo]

Primarily the changes requested are to not remove package.json files from each of the examples, this is so that developers can copy and paste an entire example folder to their and do not have to worry about trying to cheery pick npm commands from the root of the project.

That is indeed a good point. I addressed it in 85274c9. I ensured that all commands managed globally can also be executed when the individual block is copied over.

I thought about adding lerna so we could run those commands from the root folder in a more simplified way, but this would prevent us from having examples of more advanced usage of wp-scripts. So, I guess it's fine as is until we have double as much ESNext bases subpackages to maintain.

[ntwb]

Thanks @gziolo 💯