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/workspace/src/pane.rs

@@ -72,7 +72,7 @@ impl DraggedSelection {
 }
 
 #[derive(Clone, Copy, PartialEq, Debug, Deserialize, JsonSchema)]
-#[serde(rename_all = "camelCase")]
+#[serde(rename_all = "snake_case")]
 pub enum SaveIntent {
     /// write all files (even if unchanged)
     /// prompt before overwriting on-disk changes
@@ -96,13 +96,13 @@ pub enum SaveIntent {
 pub struct ActivateItem(pub usize);
 
 #[derive(Clone, PartialEq, Debug, Deserialize, JsonSchema, Default)]
-#[serde(rename_all = "camelCase")]
+#[serde(deny_unknown_fields)]
 pub struct CloseActiveItem {
     pub save_intent: Option<SaveIntent>,
 }
 
 #[derive(Clone, PartialEq, Debug, Deserialize, JsonSchema, Default)]
-#[serde(rename_all = "camelCase")]
+#[serde(deny_unknown_fields)]
 pub struct CloseInactiveItems {
     pub save_intent: Option<SaveIntent>,
     #[serde(default)]
@@ -110,7 +110,7 @@ pub struct CloseInactiveItems {
 }
 
 #[derive(Clone, PartialEq, Debug, Deserialize, JsonSchema, Default)]
-#[serde(rename_all = "camelCase")]
+#[serde(deny_unknown_fields)]
 pub struct CloseAllItems {
     pub save_intent: Option<SaveIntent>,
     #[serde(default)]
@@ -118,34 +118,35 @@ pub struct CloseAllItems {
 }
 
 #[derive(Clone, PartialEq, Debug, Deserialize, JsonSchema, Default)]
-#[serde(rename_all = "camelCase")]
+#[serde(deny_unknown_fields)]
 pub struct CloseCleanItems {
     #[serde(default)]
     pub close_pinned: bool,
 }
 
 #[derive(Clone, PartialEq, Debug, Deserialize, JsonSchema, Default)]
-#[serde(rename_all = "camelCase")]
+#[serde(deny_unknown_fields)]
 pub struct CloseItemsToTheRight {
     #[serde(default)]
     pub close_pinned: bool,
 }
 
 #[derive(Clone, PartialEq, Debug, Deserialize, JsonSchema, Default)]
-#[serde(rename_all = "camelCase")]
+#[serde(deny_unknown_fields)]
 pub struct CloseItemsToTheLeft {
     #[serde(default)]
     pub close_pinned: bool,
 }
 
 #[derive(Clone, PartialEq, Debug, Deserialize, JsonSchema, Default)]
-#[serde(rename_all = "camelCase")]
+#[serde(deny_unknown_fields)]
 pub struct RevealInProjectPanel {
     #[serde(skip)]
     pub entry_id: Option<u64>,
 }
 
 #[derive(Clone, PartialEq, Debug, Deserialize, JsonSchema, Default)]
+#[serde(deny_unknown_fields)]
 pub struct DeploySearch {
     #[serde(default)]
     pub replace_enabled: bool,