Show error and warning indicators in tabs (#21383)

Closes #21179

Release Notes:

- Add setting to display error and warning indicators in tabs.

<img width="454" alt="demo_with_icons"
src="https://github.com/user-attachments/assets/6002b4d4-dca8-4e2a-842d-1df3e281fcd2">
<img width="454" alt="demo_without_icons"
src="https://github.com/user-attachments/assets/df4b67bd-1a6c-4354-847e-d7fea95c1b7e">

crates/workspace/src/item.rs

@@ -42,6 +42,7 @@ pub struct ItemSettings {
     pub close_position: ClosePosition,
     pub activate_on_close: ActivateOnClose,
     pub file_icons: bool,
+    pub show_diagnostics: ShowDiagnostics,
     pub always_show_close_button: bool,
 }
 
@@ -60,6 +61,15 @@ pub enum ClosePosition {
     Right,
 }
 
+#[derive(Copy, Clone, Debug, Default, Serialize, Deserialize, JsonSchema, PartialEq, Eq)]
+#[serde(rename_all = "snake_case")]
+pub enum ShowDiagnostics {
+    Off,
+    Errors,
+    #[default]
+    All,
+}
+
 #[derive(Clone, Default, Serialize, Deserialize, JsonSchema)]
 #[serde(rename_all = "lowercase")]
 pub enum ActivateOnClose {
@@ -86,6 +96,11 @@ pub struct ItemSettingsContent {
     ///
     /// Default: history
     pub activate_on_close: Option<ActivateOnClose>,
+    /// Which files containing diagnostic errors/warnings to mark in the tabs.
+    /// This setting can take the following three values:
+    ///
+    /// Default: all
+    show_diagnostics: Option<ShowDiagnostics>,
     /// Whether to always show the close button on tabs.
     ///
     /// Default: false