- defaults to depth and stencil tests off
- whether or not depth and stencil tests are enabled is inferred from the comparison functions and stencil operations
- only one stencil reference. D3D12 does not support separate references
- change SetDepthWriteMode to SetDepthWriteEnabled and use a bool instead of enum
- Create PersistentPipelineState class for OpenGL backend with simple state tracking
- Add validation so DepthStencilState properties are only set once
- Update API usage in HelloDepthStencil
- refactor tracking of the DepthStencilState in the Metal backend
- validate that compute pipeline does not have a depth stencil state
* First API design (many features missing, including input attachments)
* Metal implementation (no OpenGL yet)
* Render-to-texture demo (a little broken until we have depth buffers)
* Update examples to use render passes
