Describe the pull request

This PR implements support for resource defragmentation. This is mostly done on the IGraphicsFactory, but also on buffers and images directly. The graphics factory now exposes a set of methods to invoke the defragmentation process. For an example implementation, a sample is provided.

Resources (i.e., objects that implement IDeviceMemory) are potentially moved during defragmentation. As this implies a re-creation of the resource itself, bindings may get invalidated. To react to such a move, there are two events that can be subscribed to. The IDeviceMemory::moving event occurs after a move has been recorded, but before it has been finished. It provides the command queue and a fence value on that queue that signals if the move has finished. On the other hand, the IDeviceMemory::moved event is more straightforward and is executed after a resource has been relocated and can be rebound.

Currently render targets aren't affected by defragmentation, as they are often times implicitly transitioned during rendering and moving them mandates some form state tracking to properly barrier them. The way this is implemented is by checking if an image has the ResourceUsage::RenderTarget flag set during a defragmentation pass and if so, it is ignored. This is sub-optimal and ideally, render targets should be allocated from a separate pool instead. If this ever becomes a problem, we can address it this way.

Related issues

• Resolves Add support for resource defragmentation. #180