GPU: Xbox alignment requirements not met

[flibitijibibo]

Xbox is annoying about resource alignment and is insistent on it being a magic number - we get it right at first but it doesn't always stick; FNA3D hits it after setting our second dummy texture data:

https://github.com/FNA-XNA/FNA3D/blob/master/src/FNA3D_Driver_SDL.c#L4472

Pretty sure we had this right at one point but resource management has probably changed a lot since our last Xbox checkup.

[flibitijibibo]

Got a better explanation: While we realign source data to match Xbox's needs, it turns out it also cares about slices being aligned too. So this increment ends up breaking the rule after slice 0:

https://github.com/libsdl-org/SDL/blob/main/src/gpu/d3d12/SDL_gpu_d3d12.c#L5762

In addition to aligned row pitch we also need aligned slice offsets, so that's fun!