## Summary
This adds an autofix for PIE800 (unnecessary spread) -- whenever we see
a `**{...}` inside another dictionary literal, just delete the `**{` and
`}` to inline the key-value pairs. So `{"a": "b", **{"c": "d"}}` becomes
just `{"a": "b", "c": "d"}`.
I have enabled this just for preview mode.
## Test Plan
Updated the preview snapshot test.