Fix layout jumps for images

[gaearon]

I've noticed the aspectRatio value here fluctuates between user-submitted measurement vs measurement on fetch. The fluctuation is small but this leads to an extra setState and potentially to tiny layout jumps. And if the aspect ratio was not specified at all, the layout jump can be significant — per each such image.

We should never layout jump in feed. So let's either use the provided aspect, or assume it's a square.

Also lets us avoid a setState.

Test Plan

Verify images show up appropriately sized, as before (try tall, wide, square images).

Comment out the = image.aspectRatio part and verify that missing measurements are handled gracefully.

Verify lightbox works in all cases.

[github-actions]

Old size	New size	Diff
8.05 MB	8.05 MB	-54 B (-0.00%)

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[mozzius]

code lgtm, though we should let Paul know we're doing this since it's a breaking change for how images work

[gaearon]

gave heads up to Paul, he's cool