The implementation previously generated a descriptor with an `initializer()`, and bound the function to the `this` context of the initializer. In native class syntax, the initializer of a descriptor is only called once, with a `this` context of the constructor, not the instance.
This commit updates the implementation so that it generates the bound function on-demand using a getter. This is the same strategy employed by ember's built-in `@action` decorator.
Unfortunately, this use of a getter means that the `@observes` decorator does not support being directly chained to `@debounce`. It throws the error "`observer must be provided a function or an observer definition`". The workaround is to put the observer on its own function, which then calls the debounced function. Given that we're aiming to reduce our usage of `@observes`, we've accepted the need for this workaround rather than spending the time to patch the implementation of `@observes`.
e08a0b509d