Add settings to control gutter elements (#7665)

The current gutter was a bit too big for my taste, so I added some
settings to change which visual elements are shown, including being able
to hide the gutter completely.

This should help with the following issues: #4963, #4382, #7422

New settings:
```json5
"gutter": {
    "line_numbers": true, // Whether line numbers are shown
    "buttons": true // Whether the code action/folding buttons are shown
}
```

The existing `git.git_gutter` setting is also taken into account when
calculating the width of the gutter.

We could also separate the display of the code action and folding
buttons into separate settings, let me know if that is desirable.

## Screenshots:

- Everything on (`gutter.line_numbers`, `gutter.buttons`,
`git.git_gutter`):
<img width="434" alt="SCR-20240210-trfb"
src="https://github.com/zed-industries/zed/assets/17355488/bcc55311-6e1d-4c22-8c43-4f364637959b">

- Only line numbers and git gutter (`gutter.line_numbers`,
`git.git_gutter`):
<img width="406" alt="SCR-20240210-trhm"
src="https://github.com/zed-industries/zed/assets/17355488/0a0e074d-64d0-437c-851b-55560d5a6c6b">

- Only git gutter (`git.git_gutter`):
<img width="356" alt="SCR-20240210-trkb"
src="https://github.com/zed-industries/zed/assets/17355488/7ebdb38d-93a5-4e38-b008-beabf355510d">

- Only git gutter and buttons (`git.git_gutter`, `gutter.buttons`):
<img width="356" alt="SCR-20240210-txyo"
src="https://github.com/zed-industries/zed/assets/17355488/e2c92c05-cc30-43bc-9399-09ea5e376e1b">


- Nothing:
<img width="350" alt="SCR-20240210-trne"
src="https://github.com/zed-industries/zed/assets/17355488/e0cd301d-c3e0-4b31-ac69-997515928b5a">



## Release Notes:
- Added settings to control the display of gutter visual elements. `"gutter": {"line_numbers": true,    "code_actions": true,    "folds": true}` ([#8041](https://github.com/zed-industries/zed/issues/8041))  ([#7422](https://github.com/zed-industries/zed/issues/7422))
```

---------

Co-authored-by: Conrad Irwin <conrad.irwin@gmail.com>

crates/editor/src/editor_settings.rs

@@ -12,6 +12,7 @@ pub struct EditorSettings {
     pub use_on_type_format: bool,
     pub toolbar: Toolbar,
     pub scrollbar: Scrollbar,
+    pub gutter: Gutter,
     pub vertical_scroll_margin: f32,
     pub relative_line_numbers: bool,
     pub seed_search_query_from_cursor: SeedQuerySetting,
@@ -45,6 +46,13 @@ pub struct Scrollbar {
     pub diagnostics: bool,
 }
 
+#[derive(Copy, Clone, Debug, Serialize, Deserialize, JsonSchema, PartialEq, Eq)]
+pub struct Gutter {
+    pub line_numbers: bool,
+    pub code_actions: bool,
+    pub folds: bool,
+}
+
 /// When to show the scrollbar in the editor.
 ///
 /// Default: auto
@@ -97,6 +105,8 @@ pub struct EditorSettingsContent {
     pub toolbar: Option<ToolbarContent>,
     /// Scrollbar related settings
     pub scrollbar: Option<ScrollbarContent>,
+    /// Gutter related settings
+    pub gutter: Option<GutterContent>,
 
     /// The number of lines to keep above/below the cursor when auto-scrolling.
     ///
@@ -157,6 +167,23 @@ pub struct ScrollbarContent {
     pub diagnostics: Option<bool>,
 }
 
+/// Gutter related settings
+#[derive(Copy, Clone, Debug, Serialize, Deserialize, JsonSchema, PartialEq, Eq)]
+pub struct GutterContent {
+    /// Whether to show line numbers in the gutter.
+    ///
+    /// Default: true
+    pub line_numbers: Option<bool>,
+    /// Whether to show code action buttons in the gutter.
+    ///
+    /// Default: true
+    pub code_actions: Option<bool>,
+    /// Whether to show fold buttons in the gutter.
+    ///
+    /// Default: true
+    pub folds: Option<bool>,
+}
+
 impl Settings for EditorSettings {
     const KEY: Option<&'static str> = None;