Support popular PHP libraries and tools

[adamziel]

Let's make sure that WordPress Playground supports the usual WordPress and PHP tools.

Remaining work

• PHPUnit support
• #1712
• #692
• #827

[swissspidy]

• wp-cli support (@swissspidy explorations)

Jus as an FYI, since this initial exploration we spent some time testing WP-CLI with SQLite and most commands just work. Only wp db and wp search-replace need some extra care. So from that side it should be all good 👍