This commit fixes a bug in the Core Graphics backend that causes a new
buffer not be shown immediately but instead use a quarter second fade
transition. This happens because the CALayer has a default action
associated with a change in the layer contents.
The problem was mitigated by wrapping the contents change in a
transaction and disabling all actions for the duration of this
transaction.
Currently the size of the buffer on macOS is interpreted in logical pixels, which
is inconsistent with the other platforms. Instead,
we should apply the same scale factor that applies to regular rendering.
