settings_ui: Add theme settings controls (#15115)

This PR adds settings controls for the theme settings.

Release Notes:

- N/A

crates/ui/src/components/numeric_stepper.rs

@@ -7,6 +7,8 @@ pub struct NumericStepper {
     value: SharedString,
     on_decrement: Box<dyn Fn(&ClickEvent, &mut WindowContext) + 'static>,
     on_increment: Box<dyn Fn(&ClickEvent, &mut WindowContext) + 'static>,
+    /// Whether to reserve space for the reset button.
+    reserve_space_for_reset: bool,
     on_reset: Option<Box<dyn Fn(&ClickEvent, &mut WindowContext) + 'static>>,
 }
 
@@ -20,10 +22,16 @@ impl NumericStepper {
             value: value.into(),
             on_decrement: Box::new(on_decrement),
             on_increment: Box::new(on_increment),
+            reserve_space_for_reset: false,
             on_reset: None,
         }
     }
 
+    pub fn reserve_space_for_reset(mut self, reserve_space_for_reset: bool) -> Self {
+        self.reserve_space_for_reset = reserve_space_for_reset;
+        self
+    }
+
     pub fn on_reset(
         mut self,
         on_reset: impl Fn(&ClickEvent, &mut WindowContext) + 'static,
@@ -48,13 +56,15 @@ impl RenderOnce for NumericStepper {
                             .icon_size(icon_size)
                             .on_click(on_reset),
                     )
-                } else {
+                } else if self.reserve_space_for_reset {
                     element.child(
                         h_flex()
                             .size(icon_size.square(cx))
                             .flex_none()
                             .into_any_element(),
                     )
+                } else {
+                    element
                 }
             })
             .child(