When rasterizing to a recorder backed canvas for SKP tracing, don’t attempt to update the raster cache. (#2983)

We could get into a situation where the second time we rasterize a picture for an SKP, the raster cache detects that the same picture is being repeated in subsequent onscreen frames and then proceeds to rasterize the contents to an offscreen texture. This not only causes an unnecessary cache entry, but also shows the cached image in the final SKP trace (which is not what was originally displayed on screen).