Introduce web-colors feature flag to enable sRGB linear blending

This is how browsers perform color management. They treat
gamma-corrected sRGB colors as if they were linear RGB.

Correctness aside, this mode is introduced for legacy reasons. Most
UI/UX tooling uses this color management as well, and many have created
an intuition about how color should behave from interacting with a
browser.

This feature flag should facilitate application development with `iced`
in those cases.

More details: https://webcolorisstillbroken.com/

graphics/src/color.rs

@@ -0,0 +1,46 @@
+//! Manage colors for shaders.
+use crate::core::Color;
+
+use bytemuck::{Pod, Zeroable};
+
+/// A color packed as 4 floats representing RGBA channels.
+#[derive(Debug, Clone, Copy, PartialEq, Zeroable, Pod)]
+#[repr(C)]
+pub struct Packed([f32; 4]);
+
+impl Packed {
+    /// Returns the internal components of the [`Packed`] color.
+    pub fn components(self) -> [f32; 4] {
+        self.0
+    }
+}
+
+/// A flag that indicates whether the renderer should perform gamma correction.
+pub const GAMMA_CORRECTION: bool = internal::GAMMA_CORRECTION;
+
+/// Packs a [`Color`].
+pub fn pack(color: impl Into<Color>) -> Packed {
+    Packed(internal::pack(color.into()))
+}
+
+#[cfg(not(feature = "web-colors"))]
+mod internal {
+    use crate::core::Color;
+
+    pub const GAMMA_CORRECTION: bool = true;
+
+    pub fn pack(color: Color) -> [f32; 4] {
+        color.into_linear()
+    }
+}
+
+#[cfg(feature = "web-colors")]
+mod internal {
+    use crate::core::Color;
+
+    pub const GAMMA_CORRECTION: bool = false;
+
+    pub fn pack(color: Color) -> [f32; 4] {
+        [color.r, color.g, color.b, color.a]
+    }
+}