Describe the pull request

This PR implements support for resource aliasing, i.e., resources that overlap at a single allocation. In order to realize this, several improvements are available:

• A new, unified allocation interface for IGraphicsFactory, based on a ResourceAllocationInfo type, that returns ResourceAllocationResults. Using this interface, it is possible to allocate all resources through a single, unified IGraphicsFactory::allocate method. An additional method that accepts multiple ResourceAllocationInfos is available, which returns a generator for allocation results. This method also accepts an optional parameter canAlias that, if set to true, allocates overlapping resources.
• To check if a set of resources can be aliased on the current hardware, the IGraphicsFactory::canAlias method is available. It can be used in combination with the IGraphicsFactory::allocate method to fallback to non-overlapped resources, if required.
• One of the most prominent use-cases for overlapping resources is to create temporary render targets. To support this, the frame buffer has been extended. First, there's now an IFrameBuffer::resizing event that is called before a resize happens. The resource aliasing sample uses this event to re-allocate aliased render targets. Second, frame buffers can be created with an additional allocation callback, which, if provided, is called to request a resource. This callback enables more flexibility for working with frame buffers. In the resource aliasing sample, it returns the overlapping render targets. It can, however, also be used to create fixed-size or otherwise different-sized render target images. If it returns nullptr, the default allocation behavior is used and a full-sized render target is created from the frame buffer.
• The internal interface for buffers and images have been redesigned, so that allocations can be shared between multiple resources.
• A sample application is available that demonstrates how to use overlapping render targets.

Related issues

• Resolves Support resource aliasing. #50
• Towards Improve memory management #171