OGL-StreamBuffer: allocate fences in StreamBuffer directly
OGL-StreamBuffer: make the SLOT calculation much easier

The size of the buffer is now power of 2, so we can use a shift instead of a division.
This was at about 2% of the global CPU usage.
OGL-StreamBuffer: move alignment to caller

Only the caller know if alignment is needed at all, so it can be skipped now.
OGL-SteamBuffer: replace size_t with u32

Yes, this matters.
We align our buffer all the the time which needs a division. u64 divisions are just so slow.