The previous code used either a `@property` with `assign, nonatomic` semantics, or a `__unsafe_unretained` (non-atomic) ivar pointer to an instance for `asyncdisplaykit_node`.
This commit changes those access so that they have the equivalent of `weak, atomic` semantics.
- `_ASDisplayView.mm`
- Removes the `_node` ivar that was qualified with `__unsafe_unretained`.
- Removes `@synthesize asyncdisplaykit_node = _node;`.
- All direct uses of `_node` were replaced with:
- Creates a strong reference via `ASDisplayNode *node = _asyncdisplaykit_node;`.
- `s/_node/node/`.
- These changes were made even if there's a single use of `_asyncdisplaykit_node` as a consistency / defensive measure so that anyone editing this code in the future does not accidentally use a `weak` reference twice.
- `ASDisplayNode.mm`
- Getters and setters for `asyncdisplaykit_node` were changed from `nonatomic, assign` semantics to the equivalent of `atomic, weak` semantics.
- `weak` semantics were implemented by using a `ASWeakProxy` object.
- `objc_setAssociatedObject` was changed from `OBJC_ASSOCIATION_ASSIGN` to `OBJC_ASSOCIATION_RETAIN` (the `atomic` version of retain).
- `ASDisplayNode+FrameworkPrivate.h`
- Changed the `@property` declarations for `asyncdisplaykit_node` from `nonatomic, assign` to `atomic, weak`.
- The actual getters and setters are implemented in `ASDisplayNode.mm`, which were changed accordingly.