settings_ui: Fix stepper buttons to Inactive Opacity to 0.1 increment adjustments (#40477)

Closes #40279

Release Notes:

- Fix stepper buttons (+/-) to the Inactive Opacity setting for 0.1
increment adjustments on settings UI

---------

Co-authored-by: Danilo Leal <daniloleal09@gmail.com>

crates/ui_input/src/number_field.rs

@@ -8,7 +8,7 @@ use std::{
 use editor::{Editor, EditorStyle};
 use gpui::{ClickEvent, Entity, FocusHandle, Focusable, FontWeight, Modifiers};
 
-use settings::{CodeFade, MinimumContrast};
+use settings::{CodeFade, InactiveOpacity, MinimumContrast};
 use ui::prelude::*;
 
 #[derive(Debug, Default, Clone, Copy, PartialEq, Eq, Hash)]
@@ -79,6 +79,30 @@ impl NumberFieldType for settings::CodeFade {
     }
 }
 
+impl NumberFieldType for settings::InactiveOpacity {
+    fn default_step() -> Self {
+        InactiveOpacity(0.10)
+    }
+    fn large_step() -> Self {
+        InactiveOpacity(0.20)
+    }
+    fn small_step() -> Self {
+        InactiveOpacity(0.05)
+    }
+    fn min_value() -> Self {
+        InactiveOpacity(0.0)
+    }
+    fn max_value() -> Self {
+        InactiveOpacity(1.0)
+    }
+    fn saturating_add(self, rhs: Self) -> Self {
+        InactiveOpacity((self.0 + rhs.0).min(Self::max_value().0))
+    }
+    fn saturating_sub(self, rhs: Self) -> Self {
+        InactiveOpacity((self.0 - rhs.0).max(Self::min_value().0))
+    }
+}
+
 impl NumberFieldType for settings::MinimumContrast {
     fn default_step() -> Self {
         MinimumContrast(1.0)