core: button: add supported keys querying to keyboard trait

src/core/button.rs

@@ -107,6 +107,8 @@ struct Press {
 const PRESSES_MAX: usize = 64;
 
 pub trait Keyboard {
+    fn key_supported(&self, sym: Keysym) -> bool;
+
     fn press(&mut self, sym: Keysym);
     fn release(&mut self, sym: Keysym);
     fn change_layout(&mut self, layout: &Layout);

src/wayland/keyboard.rs

@@ -89,6 +89,14 @@ impl VirtualKeyboard {
 }
 
 impl Keyboard for VirtualKeyboard {
+    fn key_supported(&self, sym: Keysym) -> bool
+    {
+        match sym.name() {
+            Some(n) => n.starts_with("XK_"),
+            None => false,
+        }
+    }
+
     fn press(&mut self, sym: Keysym)
     {
         if sym == Keysym::NoSymbol || sym == Keysym::XF86_Fn {