feat: implement SegmentedButton widget

src/widget/segmented_button/style.rs

@@ -0,0 +1,29 @@
+/// Copyright 2022 System76 <info@system76.com>
+// SPDX-License-Identifier: MPL-2.0
+
+use iced_core::{Background, BorderRadius, Color};
+
+/// The appearance of a [`SegmentedButton`].
+#[derive(Clone, Copy)]
+pub struct Appearance {
+    pub button_active: ButtonAppearance,
+    pub button_inactive: ButtonAppearance,
+}
+
+/// The appearance of a button in the [`SegmentedButton`]
+#[derive(Clone, Copy)]
+pub struct ButtonAppearance {
+    pub background: Option<Background>,
+    pub border_radius: BorderRadius,
+    pub border_bottom: Option<(f32, Color)>,
+    pub text_color: Color,
+}
+
+/// Defines the [`Appearance`] of a [`SegmentedButton`].
+pub trait StyleSheet {
+    /// The supported style of the [`StyleSheet`].
+    type Style: Default;
+
+    /// The [`Appearance`] of the [`SegmentedButton`].
+    fn appearance(&self, style: &Self::Style) -> Appearance;
+}