Respect label_color for Buttons (#3469)

This PR makes `Button`s respect the `label_color` that is specified,
provided they are not disabled or selected.

Release Notes:

- N/A

crates/ui2/src/components/button/button.rs

@@ -79,7 +79,7 @@ impl RenderOnce for Button {
         } else if self.base.selected {
             Color::Selected
         } else {
-            Color::Default
+            self.label_color.unwrap_or_default()
         };
 
         self.base.child(

crates/ui2/src/components/stories/button.rs

@@ -14,6 +14,10 @@ impl Render for ButtonStory {
             .child(Story::title_for::<Button>())
             .child(Story::label("Default"))
             .child(Button::new("default_filled", "Click me"))
+            .child(Story::label("Selected"))
+            .child(Button::new("selected_filled", "Click me").selected(true))
+            .child(Story::label("With `label_color`"))
+            .child(Button::new("filled_with_label_color", "Click me").color(Color::Created))
             .child(Story::label("Default (Subtle)"))
             .child(Button::new("default_subtle", "Click me").style(ButtonStyle::Subtle))
             .child(Story::label("Default (Transparent)"))