This directory used to contain both the state tracking code for the
backends, and the common utilities that could be used both by the
backends and the rest of the code. Things are now:
- src/common is utility code for the whole repo
- src/backend contains libNXT's code
- src/utils is utility code that we don't want in libNXT
This commit also changes all includes to use global paths from src/
bacause it had to touch a bunch of #include statements anyway.
- 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
