git_ui: Add Git Panel settings (#23132)

This PR adds settings for the Git Panel.

The new settings include:

| Setting | Description | Default |
|---------|-------------|---------|
| `git_panel.button` | Toggle visibility of the Git Panel button in the
status bar | `true` |
| `git_panel.dock` | Choose where to dock the Git Panel | `"left"` |
| `git_panel.default_width` | Set the default width of the Git Panel in
pixels | `360` |
| `git_panel.status_style` | Select how Git status is displayed |
`"icon"` |
| `git_panel.scrollbar.show` | Configure scrollbar behavior | Inherits
from editor settings |

Example usage:

```json
"git_panel": {
  "button": true,
  "dock": "left",
  "default_width": 360,
  "status_style": "icon",
  "scrollbar": {
    "show": "auto"
  }
}
```

Release Notes:

- N/A

crates/git_ui/src/git_panel_settings.rs

@@ -0,0 +1,83 @@
+use editor::ShowScrollbar;
+use gpui::Pixels;
+use schemars::JsonSchema;
+use serde_derive::{Deserialize, Serialize};
+use settings::{Settings, SettingsSources};
+use workspace::dock::DockPosition;
+
+#[derive(Copy, Clone, Debug, Serialize, Deserialize, JsonSchema, PartialEq, Eq)]
+pub struct ScrollbarSettingsContent {
+    /// When to show the scrollbar in the git panel.
+    ///
+    /// Default: inherits editor scrollbar settings
+    pub show: Option<Option<ShowScrollbar>>,
+}
+
+#[derive(Copy, Clone, Debug, Serialize, Deserialize, JsonSchema, PartialEq, Eq)]
+pub struct ScrollbarSettings {
+    pub show: Option<ShowScrollbar>,
+}
+
+#[derive(Copy, Clone, Debug, Serialize, Deserialize, JsonSchema, PartialEq, Eq)]
+#[serde(rename_all = "snake_case")]
+// Style of the git status indicator in the panel.
+//
+// Default: icon
+pub enum StatusStyleContent {
+    Icon,
+    LabelColor,
+}
+
+#[derive(Default, Copy, Clone, Debug, Serialize, Deserialize, JsonSchema, PartialEq, Eq)]
+#[serde(rename_all = "snake_case")]
+pub enum StatusStyle {
+    #[default]
+    Icon,
+    LabelColor,
+}
+
+#[derive(Clone, Default, Serialize, Deserialize, JsonSchema, Debug)]
+pub struct GitPanelSettingsContent {
+    /// Whether to show the panel button in the status bar.
+    ///
+    /// Default: true
+    pub button: Option<bool>,
+    /// Where to dock the panel.
+    ///
+    /// Default: left
+    pub dock: Option<DockPosition>,
+    /// Default width of the panel in pixels.
+    ///
+    /// Default: 360
+    pub default_width: Option<f32>,
+    /// How entry statuses are displayed.
+    ///
+    /// Default: icon
+    pub status_style: Option<StatusStyle>,
+    /// How and when the scrollbar should be displayed.
+    ///
+    /// Default: inherits editor scrollbar settings
+    pub scrollbar: Option<ScrollbarSettings>,
+}
+
+#[derive(Deserialize, Debug, Clone, Copy, PartialEq)]
+pub struct GitPanelSettings {
+    pub button: bool,
+    pub dock: DockPosition,
+    pub default_width: Pixels,
+    pub status_style: StatusStyle,
+    pub scrollbar: ScrollbarSettings,
+}
+
+impl Settings for GitPanelSettings {
+    const KEY: Option<&'static str> = Some("git_panel");
+
+    type FileContent = GitPanelSettingsContent;
+
+    fn load(
+        sources: SettingsSources<Self::FileContent>,
+        _: &mut gpui::AppContext,
+    ) -> anyhow::Result<Self> {
+        sources.json_merge()
+    }
+}