Vulkan AS rebuild-on-replay: Serialise and Replay

The VkAccelerationStructureInfo structure is serialised followed by the unified geometry readback buffer.

When the initial state Apply() is called the ASes are built from the input data one at a time so that a single scratch buffer can be built (enlarging when needed) and re-used.  Although this is slower it is necessary on Mali as it has poor space efficiency for the scratch buffer and so can easily OOM a device if all the ASes are built in a single command buffer submission.