Update outline panel representation when a theme is changed (#19747)

Release Notes:

- N/A

crates/theme/src/settings.rs

@@ -86,7 +86,7 @@ impl From<UiDensity> for String {
 }
 
 /// Customizable settings for the UI and theme system.
-#[derive(Clone)]
+#[derive(Clone, PartialEq)]
 pub struct ThemeSettings {
     /// The UI font size. Determines the size of text in the UI,
     /// as well as the size of a [gpui::Rems] unit.
@@ -213,7 +213,7 @@ pub(crate) struct AdjustedUiFontSize(Pixels);
 impl Global for AdjustedUiFontSize {}
 
 /// Represents the selection of a theme, which can be either static or dynamic.
-#[derive(Clone, Debug, Serialize, Deserialize, JsonSchema)]
+#[derive(Clone, Debug, Serialize, Deserialize, JsonSchema, PartialEq, Eq)]
 #[serde(untagged)]
 pub enum ThemeSelection {
     /// A static theme selection, represented by a single theme name.