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.
Buffers with MapRead allowed are created on the READBACK heap and always
add the D3D12_RESOURCE_STATE_COPY_DEST state (required by D3D12).
Likewise MapWrite adds the D3D12_RESOURCE_STATE_GENERIC_READ state and
places resources on the UPLOAD heap. Because these states are
required, transitions for mapped buffers do nothing.
