editor: Current line highlight options (#11710)

None:

<img width="717" alt="none"
src="https://github.com/zed-industries/zed/assets/2101250/b2a741db-c64a-4275-a612-5a0d15c9cab7">

Gutter:

<img width="715" alt="gutter"
src="https://github.com/zed-industries/zed/assets/2101250/f7a68a6e-6eba-41b4-9042-5a5fe2ee21a4">

Line:

<img width="717" alt="line"
src="https://github.com/zed-industries/zed/assets/2101250/117f5b00-abd7-425b-8047-1a6fab8293a7">

All:

<img width="715" alt="all"
src="https://github.com/zed-industries/zed/assets/2101250/ebccc0da-0fa0-44e5-903c-cc49d975db76">

This PR adds the `current_line_highlight` setting that defines how to
highlight the current line in the editor:

- `none`: Don't highlight the current line.
- `gutter`: Highlight the gutter area only.
- `line`: Highlight the editor area only.
- `all` (default): Highlight the whole line.

The options have been borrowed from VSCode.

Fixes #5222
Part of #4382

Release Notes:

- Added the `current_line_highlight` setting that defines how to
highlight the current line in the editor (#5222).

crates/editor/src/editor_settings.rs

@@ -6,6 +6,7 @@ use settings::{Settings, SettingsSources};
 #[derive(Deserialize, Clone)]
 pub struct EditorSettings {
     pub cursor_blink: bool,
+    pub current_line_highlight: CurrentLineHighlight,
     pub hover_popover_enabled: bool,
     pub show_completions_on_input: bool,
     pub show_completion_documentation: bool,
@@ -24,6 +25,19 @@ pub struct EditorSettings {
     pub double_click_in_multibuffer: DoubleClickInMultibuffer,
 }
 
+#[derive(Copy, Clone, Debug, Serialize, Deserialize, PartialEq, Eq, JsonSchema)]
+#[serde(rename_all = "snake_case")]
+pub enum CurrentLineHighlight {
+    // Don't highlight the current line.
+    None,
+    // Highlight the gutter area.
+    Gutter,
+    // Highlight the editor area.
+    Line,
+    // Highlight the full line.
+    All,
+}
+
 /// When to populate a new search's query based on the text under the cursor.
 #[derive(Copy, Clone, Debug, Serialize, Deserialize, PartialEq, Eq, JsonSchema)]
 #[serde(rename_all = "snake_case")]
@@ -105,6 +119,10 @@ pub struct EditorSettingsContent {
     ///
     /// Default: true
     pub cursor_blink: Option<bool>,
+    /// How to highlight the current line in the editor.
+    ///
+    /// Default: all
+    pub current_line_highlight: Option<CurrentLineHighlight>,
     /// Whether to show the informational hover box when moving the mouse
     /// over symbols in the editor.
     ///