New Unit Test: Register/Unregister hooks

We need tests to ensure our `register_activation_hook` and `register_deactivation_hook`s are firing as expected on plugin activation/deactivation.

Not sure the best way to do it, but can we write a test that just uses the two functions and hard-code the jetpack.php path in the first param? Something like

`register_activation_hook( jetpack.php, array( $this, 'set_some_test_option' ) );`
`register_deactivation_hook( jetpack.php, array( $this, 'delete_some_test_option' ) );`

and somewhere in there also use core functions to activate/deactivate?

Otherwise, it should be a straightforward E2E

Related bug: #13058

Start with the register_activation_hook and register_deactivation_hook entry points and the proposed jetpack.php path. Check how WordPress core activation and deactivation functions can invoke those hooks, then determine whether a unit test or E2E test is appropriate. Done means tests demonstrate both hooks fire during plugin activation and deactivation.

Written by the indexing model from the issue text.