Clean up the behavior tests (facebook#5365)

* Speed up installs with pnp

* Move to a better relative path test

* Continue work on new test organization

* Move mjs test to new enhanced tests

* Move over last legacy test

* Update behavior e2e script

* Add first iteration of instructions to test readme

* Add some more bad instructions

* Split test command into multiple lines

* Use two workers (do not run in band)

* Bump install timeout

* No global pollution

* Fix PnP support via standard run mechanism

* Prevent circular serve command

* Silent yarn execs

* Fix common commands by using a shell

* Run with npx instead of Yarn

* Remove unused scripts

* Wait for localhost and fix script booting with PnP

* Don't pnp locally because links will cause module resolution to whine

* lint-staged is annoying

* Strip Yarn out of execa runs

* Set default license if none specified

* Don't impose worker limit

* Disable pnp for webpack messages

* Add missing dependency

* Disable timeout and rely on Jest

* Only use 2 jest workers

* Add missing dependency

Author: Timer