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.rs

@@ -88,6 +88,7 @@ pub use multi_buffer::{
 };
 use ordered_float::OrderedFloat;
 use parking_lot::{Mutex, RwLock};
+use project::project_settings::{GitGutterSetting, ProjectSettings};
 use project::{FormatTrigger, Location, Project, ProjectPath, ProjectTransaction};
 use rand::prelude::*;
 use rpc::proto::*;
@@ -443,7 +444,8 @@ pub struct EditorSnapshot {
 }
 
 pub struct GutterDimensions {
-    pub padding: Pixels,
+    pub left_padding: Pixels,
+    pub right_padding: Pixels,
     pub width: Pixels,
     pub margin: Pixels,
 }
@@ -451,7 +453,8 @@ pub struct GutterDimensions {
 impl Default for GutterDimensions {
     fn default() -> Self {
         Self {
-            padding: Pixels::ZERO,
+            left_padding: Pixels::ZERO,
+            right_padding: Pixels::ZERO,
             width: Pixels::ZERO,
             margin: Pixels::ZERO,
         }
@@ -4058,7 +4061,8 @@ impl Editor {
         if self.available_code_actions.is_some() {
             Some(
                 IconButton::new("code_actions_indicator", ui::IconName::Bolt)
-                    .icon_size(IconSize::Small)
+                    .icon_size(IconSize::XSmall)
+                    .size(ui::ButtonSize::None)
                     .icon_color(Color::Muted)
                     .selected(is_active)
                     .on_click(cx.listener(|editor, _e, cx| {
@@ -9636,23 +9640,50 @@ impl EditorSnapshot {
         max_line_number_width: Pixels,
         cx: &AppContext,
     ) -> GutterDimensions {
-        if self.show_gutter {
-            let descent = cx.text_system().descent(font_id, font_size);
-            let gutter_padding_factor = 4.0;
-            let gutter_padding = (em_width * gutter_padding_factor).round();
+        if !self.show_gutter {
+            return GutterDimensions::default();
+        }
+        let descent = cx.text_system().descent(font_id, font_size);
+
+        let show_git_gutter = matches!(
+            ProjectSettings::get_global(cx).git.git_gutter,
+            Some(GitGutterSetting::TrackedFiles)
+        );
+        let gutter_settings = EditorSettings::get_global(cx).gutter;
+
+        let line_gutter_width = if gutter_settings.line_numbers {
             // Avoid flicker-like gutter resizes when the line number gains another digit and only resize the gutter on files with N*10^5 lines.
             let min_width_for_number_on_gutter = em_width * 4.0;
-            let gutter_width =
-                max_line_number_width.max(min_width_for_number_on_gutter) + gutter_padding * 2.0;
-            let gutter_margin = -descent;
-
-            GutterDimensions {
-                padding: gutter_padding,
-                width: gutter_width,
-                margin: gutter_margin,
-            }
+            max_line_number_width.max(min_width_for_number_on_gutter)
         } else {
-            GutterDimensions::default()
+            0.0.into()
+        };
+
+        let left_padding = if gutter_settings.code_actions {
+            em_width * 3.0
+        } else if show_git_gutter && gutter_settings.line_numbers {
+            em_width * 2.0
+        } else if show_git_gutter || gutter_settings.line_numbers {
+            em_width
+        } else {
+            px(0.)
+        };
+
+        let right_padding = if gutter_settings.folds && gutter_settings.line_numbers {
+            em_width * 4.0
+        } else if gutter_settings.folds {
+            em_width * 3.0
+        } else if gutter_settings.line_numbers {
+            em_width
+        } else {
+            px(0.)
+        };
+
+        GutterDimensions {
+            left_padding,
+            right_padding,
+            width: line_gutter_width + left_padding + right_padding,
+            margin: -descent,
         }
     }
 }
@@ -10159,9 +10190,14 @@ pub fn diagnostic_block_renderer(diagnostic: Diagnostic, _is_valid: bool) -> Ren
             .group(group_id.clone())
             .relative()
             .size_full()
-            .pl(cx.gutter_width)
-            .w(cx.max_width + cx.gutter_width)
-            .child(div().flex().w(cx.anchor_x - cx.gutter_width).flex_shrink())
+            .pl(cx.gutter_dimensions.width)
+            .w(cx.max_width + cx.gutter_dimensions.width)
+            .child(
+                div()
+                    .flex()
+                    .w(cx.anchor_x - cx.gutter_dimensions.width)
+                    .flex_shrink(),
+            )
             .child(div().flex().flex_shrink_0().child(
                 StyledText::new(text_without_backticks.clone()).with_highlights(
                     &text_style,