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>

crates/vim/src/object.rs

@@ -19,6 +19,7 @@ use serde::Deserialize;
 use ui::Context;
 
 #[derive(Copy, Clone, Debug, PartialEq, Eq, Deserialize, JsonSchema)]
+#[serde(rename_all = "snake_case")]
 pub enum Object {
     Word { ignore_punctuation: bool },
     Subword { ignore_punctuation: bool },
@@ -44,20 +45,20 @@ pub enum Object {
 }
 
 #[derive(Clone, Deserialize, JsonSchema, PartialEq)]
-#[serde(rename_all = "camelCase")]
+#[serde(deny_unknown_fields)]
 struct Word {
     #[serde(default)]
     ignore_punctuation: bool,
 }
 
 #[derive(Clone, Deserialize, JsonSchema, PartialEq)]
-#[serde(rename_all = "camelCase")]
+#[serde(deny_unknown_fields)]
 struct Subword {
     #[serde(default)]
     ignore_punctuation: bool,
 }
 #[derive(Clone, Deserialize, JsonSchema, PartialEq)]
-#[serde(rename_all = "camelCase")]
+#[serde(deny_unknown_fields)]
 struct IndentObj {
     #[serde(default)]
     include_below: bool,