Linux/BSD: Modify only keypad keys

The `keycode` field of `InputEventKey` is supposed to be "unshifted";
That is, what the key would output if no modifier keys were pressed.
This should match what's written on the key label, but `Key` enumerates
also all keypad keys, which require a modifier. We thus require some
extra checks for them.

Note that this can still allow "stuck keys", but that's an even deeper
problem.

platform/linuxbsd/wayland/key_mapping_xkb.h

@@ -56,6 +56,7 @@ class KeyMappingXKB {
 public:
 	static void initialize();
 
+	static bool is_sym_numpad(xkb_keysym_t p_keysym);
 	static Key get_keycode(xkb_keysym_t p_keysym);
 	static xkb_keycode_t get_xkb_keycode(Key p_keycode);
 	static Key get_scancode(unsigned int p_code);