Instead of getting the whole text from the buffer, replacing with
`String::replace`, and getting a whole diff, we'll now use `SearchQuery`
to get a range, diff only that range, and apply it (all in the
background).

When we match zero strings, we'll record a "bad search", keep going and
report it to the model at the end.

Release Notes:

- N/A

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Co-authored-by: Max <max@zed.dev>