This removes the following for both Buffer and Texture:
- The builder's SetInitialUsage
- The object's FreezeUsage and TransitionUsage methods
- The CommandBuffer Transition<Object>Usage methods
All samples and tests are simplified as a result. This also obsoletes
the UsageValidationTest which is removed.
Some validation was dependent on "current usage" and hasn't been
reintroduced for implicit transitions yet:
- Buffers can be used while mapped
- Swapchain textures can be used after they have been presented.
Validation for these will involve collecting all the resources used by a
command buffer and will be done in a follow-up patch.
