Replace postinstall bash script with a node script (better support for Windows)

[evanmwillhite]

Moving from Emulsify Gulp as this affects the package.json file here. Also, bumping this up in priority as build tools are not liking it either.

Original issue comment from @infiniteluke:

You may want to consider writing a small node script using https://www.npmjs.com/package/fs-extra and https://www.npmjs.com/package/cross-spawn so that emulsify will work on windows machines.

[dasginganinja]

A question for thought:

Since you are using composer to install PL, would it make sense to create composer post-install-cmd equivalents for those scripts? It just seems the yarn post-install all relies on composer being executed and could be theoretically be ran before yarn install, not even affecting the current install process.

I'm currently using Lando with a separate node service with gulp/yarn and php/composer binaries are not available. I think logically it would make sense to have PHP perform those operations as part of the initial composer install.

If that's the route you choose to go, I should be able to contribute this functionality.