This extension allows apps to provide a hint to the presentation engine
indicating which parts of the surface need updating. To provide this
hint, we call `-[CALayer setNeedsDisplayInRect:]`, which indicates that
only the given rectangle needs updating.
I'm not sure if this will have any effect, especially if
`CAMetalLayer.presentsWithTransaction` is `NO`. Luckily for us, this is
only a hint, and it is permissible for the presentation engine to do
nothing with the hint.
The tests don't work because they apparently can't handle
`VK_SUBOPTIMAL_KHR` being returned.
3914b0f07d