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.toml

@@ -81,6 +81,7 @@ members = [
     "crates/markdown_preview",
     "crates/media",
     "crates/menu",
+    "crates/migrator",
     "crates/multi_buffer",
     "crates/node_runtime",
     "crates/notifications",
@@ -279,6 +280,7 @@ markdown = { path = "crates/markdown" }
 markdown_preview = { path = "crates/markdown_preview" }
 media = { path = "crates/media" }
 menu = { path = "crates/menu" }
+migrator = { path = "crates/migrator" }
 multi_buffer = { path = "crates/multi_buffer" }
 node_runtime = { path = "crates/node_runtime" }
 notifications = { path = "crates/notifications" }