Fix SXS video batching.
Fix SXS video batching.

Previously the regular video source batched replay commands by 32
workers, but the side by side source just used a waitgroup to request
all of them at once. This ran into an unfortunate issue with Vulkan
replays in particular where memory would run out and we would get only
empty replay frames back. The fix is to use similar batching logic when
requesting frames in the side by side video source.

pmuetschard/gapid,google/gapid,Qining/gapid,google/gapid,google/gapid,baldwinn860/gapid,pmuetschard/gapid,google/agi,google/gapid,pmuetschard/gapid,baldwinn860/gapid,google/agi,pmuetschard/gapid,google/gapid,pmuetschard/gapid,google/agi,Qining/gapid,baldwinn860/gapid,baldwinn860/gapid,Qining/gapid,google/agi,pmuetschard/gapid,pmuetschard/gapid,google/agi,baldwinn860/gapid,Qining/gapid,google/gapid,google/gapid,Qining/gapid,Qining/gapid,pmuetschard/gapid,baldwinn860/gapid,google/agi,google/gapid,google/agi,baldwinn860/gapid,google/agi,Qining/gapid,Qining/gapid,baldwinn860/gapid