* Issue was that the DummyNotificationCenterDelegate was going out of
scope and getting removed.
   - This created an issue where OneSignal swizzling was no longer
   wroking, which broke any notification open tests.

* Moved swizzling logic in setOneSignalUNDelegate into
swizzleSelectorsOnDelegate
   - No logic changes just a move.
* This cleans up code a bit and also makes it more testable.

* Added this method on a new helper to undo swizzling in test
* This way there is zero carry over side-effects on other tests

* Moved this test into it's own testing file.
   - We will be adding more swizzling tests in (a) up comming commit(s)

* Moved registerAsUNNotificationCenterDelegate out of OneSignalHelper
and into OneSignalUNUserNotificationCenter
   - This better encapsulates this logic
* Added a new setup method that OneSignal class.
   - Before OneSignal had to call two methods which as client
   shouldn't have to know or care about it at that level.

* OneSignal is normally loaded into memory and it performs swizzling
before any code is exlcude as it happens in +load.
This is not always the case however so this simulates so other
code winning the setDelegate race.
* Added putIntoPreloadedState helper to simulate OneSignal class
not being loaded into memory yet.

* This happens when another library's delegate is
loaded before OneSignal's delegate code.
* This commit solves it by reassigning the pre loaded
delegate to swizzle in OneSignal's logic

* Updated the comment to better fit what we added in the else
statement from our last commit.