Fixed observer race condition

[stephenth0ma5]

Background

• In some edge cases we are observing issues with properly removing the observer because of reliance on superview and isObservingScrollView resulting in observed values getting emitted with no message handler. This ultimately results in a crash.

Changes

• Instead of relying on superview to remove the observer we can set the observer ourselves when it gets created. This eliminates the need to check if its of type UIScrollView and also eliminates the need for isObservingScrollView since we can use the class-level observer to check if one is set before removing it