Prioritize exact matches in autocompletions

[JosephTLyons]

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• Completed

Describe the bug / provide steps to reproduce it

We've had various issues come up where users type in some text and the exact match of that text is ranked further down than other matches that aren't exact:

• Implement Symbol Search / Autocomplete Sorting by Relevance #4327
• Autocomplete not showing best options first #4400
• Sort ShowCompletions results #11861
• Autocomplete order is not correct. #12280
• Autocomplete prioritises the less exact match. #19071

My initial instinct here is that these are all the same, so I've grouped them all into this issue, but I'm not entirely sure, so I haven't closed any of them out in favor of a single issue. Someone on the team can dig into this and we can adjust things accordingly after we know more.

Environment

Zed: v0.139.0 (Zed Nightly c5b22ee)
OS: macOS 14.4.0
Memory: 64 GiB
Architecture: aarch64

If applicable, add mockups / screenshots to help explain present your vision of the feature

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If applicable, attach your ~/Library/Logs/Zed/Zed.log file to this issue.

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