This is the final change for the new actions framework, covering the extension hooks and unit tests. I've repurposed the old `ActionHook` (which was just used as a generic base class) to be the new entry point for actions. This simply takes a list of `BaseAction` instances and handles registering and unregistering as appropriate. The old legacy action hooks have been updated to translate the dictionary definitions into BaseAction instances, which are then passed upward to the ActionHook base class. These are all now treated as deprecated, and will warn appropriately. This also fixes up a variety of issues discovered with the unit tests. The majority of these fixes are in the extension tests, but this also involved updating the review request actions to use `apply_to` to limit their rendering so that we wouldn't attempt to render their JavaScript side on pages that were not review-request related. Testing Done: - Built an extension that used all of the hooks, both the modern and legacy. Saw that everything worked appropriately. - Ran python unit tests. - Ran js-tests. - Built codebase and manual documentation and checked all related pages for content and spelling.