This ensures memory cleanup happens correctly and introduces a new test project
to support developing new features while stressing tough use cases for correctness.
1) Set the ascender/descender of an ASTextNode when the attributeString is set. Previously ascender/descender were only being computed in `setValuesFromLayoutable` and only when the attribute string was not nil. May make sense to remove the computation from `setValuesFromLayoutable` entirely.
2) Remove ability to allow different children of a stack spec to aling to different baselines. This wasn't working before and I'm not convinced it is possible to do properly/useful enough to invest the time.
3) Have all stack spec run `ASStackBaselinePositionedLayout::compute` to compute the stack's ascender and descender. Even if the stack isn't aligning its children to a baseline, the stack itself may be a child of another stack that IS aligning to a baseline.
This provides internal features on _ASAsyncTransaction and ASDisplayNode to facilitate
implementing public API that allows clients to choose if they would prefer to block
on the completion of unfinished rendering, rather than allow a placeholder state to
become visible.
The internal features are:
-[_ASAsyncTransaction waitUntilComplete]
-[ASDisplayNode recursivelyEnsureDisplay]
Also provided are two such implementations:
-[ASCellNode setNeverShowPlaceholders:], which integrates with both Tables and Collections
-[ASViewController setNeverShowPlaceholders:], which should work with Nav and Tab controllers.
Lastly, on ASDisplayNode, a new property .shouldBypassEnsureDisplay allows individual node types
to exempt themselves from blocking the main thread on their display.
By implementing the feature at the ASCellNode level rather than ASTableView & ASCollectionView,
developers can retain fine-grained control on display characteristics. For example, certain
cell types may be appropriate to display to the user with placeholders, whereas others may not.
Follow-up work will include unit tests, revisiting names, and the header locations of definitions.
Currently, subnodes of nodes marked with shouldRasterizeSubnodes do not get layout calls. This adds the call to layout and changes the __layout method to reference self.bounds instead of _layer.bounds.
Also adds support for corner radius when rasterizing subnodes.
