Migrate keymap and settings + edit predictions rename (#23834)

- [x] snake case keymap properties
- [x] flatten actions
- [x] keymap migration + notfication
- [x] settings migration + notification
- [x] inline completions -> edit predictions 

### future: 
- keymap notification doesn't show up on start up, only on keymap save.
this is existing bug in zed, will be addressed in seperate PR.

Release Notes:

- Added a notification for deprecated settings and keymaps, allowing you
to migrate them with a single click. A backup of your existing keymap
and settings will be created in your home directory.
- Modified some keymap actions and settings for consistency.

---------

Co-authored-by: Piotr Osiewicz <piotr@zed.dev>
Co-authored-by: Max Brunsfeld <maxbrunsfeld@gmail.com>

Cargo.lock

@@ -7836,6 +7836,17 @@ dependencies = [
  "paste",
 ]
 
+[[package]]
+name = "migrator"
+version = "0.1.0"
+dependencies = [
+ "collections",
+ "convert_case 0.7.1",
+ "pretty_assertions",
+ "tree-sitter",
+ "tree-sitter-json",
+]
+
 [[package]]
 name = "mimalloc"
 version = "0.1.43"
@@ -11980,6 +11991,7 @@ dependencies = [
  "gpui",
  "indoc",
  "log",
+ "migrator",
  "paths",
  "pretty_assertions",
  "release_channel",