send_unicode_string(): Add support for code points > 0xFFFF (#8236)

quantum/process_keycode/process_unicode_common.h

@@ -79,6 +79,7 @@ void unicode_input_finish(void);
 void unicode_input_cancel(void);
 
 void register_hex(uint16_t hex);
+void register_hex32(uint32_t hex);
 void send_unicode_hex_string(const char *str);
 void send_unicode_string(const char *str);