Adjust the max number of async blobs per transaction

[nical]

It's currently 64 and that's way too low in general especially with the small tile size we use. This will increase scene builds but hopefully reduce jank caused by lazily rasterized blobs on the render backend thread.

[nical]

Relevant irc comment by @mattwoodrow:

We could probably detect the case where we repeatedly update and rasterize a given blob without actually using it, should be easier than doing 'real visibility calculations