JSON based migrations (#39398)

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 ...

---------

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

Cargo.lock

@@ -9688,6 +9688,9 @@ dependencies = [
  "convert_case 0.8.0",
  "log",
  "pretty_assertions",
+ "serde_json",
+ "serde_json_lenient",
+ "settings",
  "streaming-iterator",
  "tree-sitter",
  "tree-sitter-json",
@@ -19686,7 +19689,6 @@ dependencies = [
  "core-foundation 0.9.4",
  "core-foundation-sys",
  "cranelift-codegen",
- "crc32fast",
  "crossbeam-channel",
  "crossbeam-epoch",
  "crossbeam-utils",