[client] overlay: show layout-translated hotkey labels

Related to #1298

client/displayservers/Wayland/input.c

@@ -225,6 +225,20 @@ done:
   close(fd);
 }
 
+bool waylandGetKeyLabel(int key, char * label, size_t size)
+{
+  if (!wlWm.xkbState)
+    return false;
+
+  key += 8; // xkb scancode is evdev scancode + 8
+  xkb_keysym_t sym = xkb_state_key_get_one_sym(wlWm.xkbState, key);
+  sym = xkb_keysym_to_upper(sym);
+
+  const uint32_t codepoint = xkb_keysym_to_utf32(sym);
+  return codepoint > 0x20 && codepoint != 0x7F &&
+    xkb_keysym_to_utf8(sym, label, size) > 0;
+}
+
 static void keyboardEnterHandler(void * data, struct wl_keyboard * keyboard,
     uint32_t serial, struct wl_surface * surface, struct wl_array * keys)
 {

client/displayservers/Wayland/wayland.c

@@ -320,6 +320,7 @@ struct LG_DisplayServerOps LGDS_Wayland =
   .uncapturePointer    = waylandUncapturePointer,
   .grabKeyboard        = waylandGrabKeyboard,
   .ungrabKeyboard      = waylandUngrabKeyboard,
+  .getKeyLabel         = waylandGetKeyLabel,
   .warpPointer         = waylandWarpPointer,
   .realignPointer      = waylandRealignPointer,
   .isValidPointerPos   = waylandIsValidPointerPos,

client/displayservers/Wayland/wayland.h

@@ -378,6 +378,7 @@ void waylandUncapturePointer(void);
 void waylandRealignPointer(void);
 void waylandWarpPointer(int x, int y, bool exiting);
 void waylandGuestPointerUpdated(double x, double y, double localX, double localY);
+bool waylandGetKeyLabel(int key, char * label, size_t size);
 // output module
 bool waylandOutputInit(void);
 void waylandOutputFree(void);