Add develop mode to Playground CLI

[jonathanbossenger]

Motivation for the change, related issues

Adds a new --develop (alias --dev) argument to the Playground CLI, which launches Playground with an opinionated set of defaults for a local development environment:

• Mounts a local directory, and installs the WordPress files in that directory if needed
• Implements the SQLite Database Integration drop-in. This is required for WP CLI commands to work on the Playground instance
• Automatically enables all WP Debug constants

Along with #3203 this allows developers to mix and match their local development requirements easily, eg:

playground-cli server --dev /path/to/new-site -x

Which would start the local development environment with Xdebug enabled

Testing Instructions

With WP CLI already installed:

• Create a new local directory with WordPress installation files wp core download --path=/path/to/new-site
• Start the playground cli server with the develop option and pass it the path to the WordPress installation: playground-cli server --dev /path/to/new-site or playground-cli server --develop /path/to/new-site
• Check that you can run WP CLI commands from the new directory (eg wp plugin list)
• Create an empty site directory `mkdir /path/to/new-site' then start the playground CLI server with the develop option and make sure it installs the WordPress files, and WP CLI works.

[adamziel]

Would it make sense to merge this into the start command? That one is also an opinionated set of defaults. We could alias it as dev for this usage:

playground-cli dev /path/to/new-site -x

[jonathanbossenger]

Would it make sense to merge this into the start command?

I was not aware there was a start command. I will look into it and see if it makes sense to simply merge them there.