Set a bigger window for `save_and_open_screenshot`
Set a bigger window for `save_and_open_screenshot`

1680x1050 is the size of a 15" retina Macbook Pro.

Without this setting, `save_and_open_screenshot` captures perhaps 75% of
the screen, which makes it much less useful for debugging.

I'm sure some people have bigger screens, and could use an even larger
window size, but this feels like a good default.

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