d3d12: fix int boundary swizzle handling

The updated CTS revealed some bugs in the correct handling of the swizzling and the boundary conditions when lowering integer texture sampling:

• the swizzle value 1 was not set correctly
• for stencil textures the swizzle was fixed to the Y channel instead of using the actual swizzle from the state and the updated swizzle information was not passed to the lowering pass so that the boundary colour could be set incorrectly