Closes #ISSUE

Adds the ability to create settings and keymap migrations by mutating
`serde_json::Value`s instead of using tree-sitter queries. This
(hopefully) will make complicated migrations far simpler to implement.

Release Notes:

- N/A *or* Added/Fixed/Improved ...

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Co-authored-by: Smit <heysmitbarmase@gmail.com>
Co-authored-by: Smit <smit@zed.dev>