Add a setting to show/hide the project panel button in the status bar (#10707)

### What?

A setting has been added to control the visibility of the Project Panel
button in the status bar.

### Why?

I don't tend to use the Project Panel, but use a keyboard shortcut to
access if needed. Thus, the button in the status bar provides me little
more than visual clutter. Additionally, there is precedent for this
configurability with other panels (collaboration, chat, notification,
terminal, etc).

Release Notes:

- Added a setting to show/hide the Project Panel button in the status
bar. `{"project_panel": {"button": false}}`

crates/project_panel/src/project_panel.rs

@@ -1899,8 +1899,10 @@ impl Panel for ProjectPanel {
         cx.notify();
     }
 
-    fn icon(&self, _: &WindowContext) -> Option<ui::IconName> {
-        Some(ui::IconName::FileTree)
+    fn icon(&self, cx: &WindowContext) -> Option<IconName> {
+        ProjectPanelSettings::get_global(cx)
+            .button
+            .then(|| IconName::FileTree)
     }
 
     fn icon_tooltip(&self, _cx: &WindowContext) -> Option<&'static str> {

crates/project_panel/src/project_panel_settings.rs

@@ -13,6 +13,7 @@ pub enum ProjectPanelDockPosition {
 
 #[derive(Deserialize, Debug, Clone, Copy, PartialEq)]
 pub struct ProjectPanelSettings {
+    pub button: bool,
     pub default_width: Pixels,
     pub dock: ProjectPanelDockPosition,
     pub file_icons: bool,
@@ -25,6 +26,10 @@ pub struct ProjectPanelSettings {
 
 #[derive(Clone, Default, Serialize, Deserialize, JsonSchema, Debug)]
 pub struct ProjectPanelSettingsContent {
+    /// Whether to show the project panel button in the status bar.
+    ///
+    /// Default: true
+    pub button: Option<bool>,
     /// Customise default width (in pixels) taken by project panel
     ///
     /// Default: 240