* Add experimental feature of hierarchyDisplayDidFinish being recursive
## Summary
`hierarchyDisplayDidFinish` is currently called when a node's immediate subnodes implement custom CALayer rendering. For example, ASNetworkImageNode and ASTextNode perform this sort of rendering. However, it can be useful -- and less fragile -- if `hierarchyDisplayDidFinish` is propagated further up the node hierarchy. That way, if a feature is refactored such that an extra node appears between the node implementing `hierarchyDisplayDidFinish` and the nodes doing CALayer rendering, we don't lose the callback.
## Test plan
Manually tested using a modified version of the Kittens example. Also ran `build.sh tests`.
* Revert SDK change since it's still Xcode 15
* Update to Xcode 15
## Summary
We want to make Texture build with recent tools like Xcode 15. Part of this is bumping the minimum supported OS to iOS 14.
I only removed the dead code (i.e. code gated on versions older than iOS 14). There are still some warnings about outdated APIs in use, but they are non-trivial changes to fix.
## Test plan
Run all the examples. Run all the unit tests and make them pass.
* Use Xcode 15.3 so we have 17.4 simulators
* Fixing an asset catalog compiler error when building against iPhone SE
* Fix a couple of file extensions for assets
A couple of PNGs were marked as JPGs
Andy Finnell