derive serde Serialize and Deserialize on `KeyboardShortcut` (#3694)

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This is a very simple change so you don't have to do this:
https://github.com/zeozeozeo/egui-keybind/blob/master/src/bind.rs#L149-L172

crates/egui/src/data/input.rs

@@ -1060,6 +1060,7 @@ impl Key {
 /// Can be used with [`crate::InputState::consume_shortcut`]
 /// and [`crate::Context::format_shortcut`].
 #[derive(Clone, Copy, Debug, Hash, PartialEq, Eq)]
+#[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
 pub struct KeyboardShortcut {
     pub modifiers: Modifiers,
     pub key: Key,