Fix and improve EXTENSIBLE_UI (#12117)

- Add methods to access print counter data
- Clean up some inconsistent method names
- Clear lcd status after filament change
- Implement `lcd_reset_status` so it works like UltraLCD

Marlin/src/lcd/extensible_ui/lib/example.cpp

@@ -0,0 +1,65 @@
+/*************
+ * dummy.cpp *
+ *************/
+
+/****************************************************************************
+ *   Written By Marcio Teixeira 2018 - Aleph Objects, Inc.                  *
+ *                                                                          *
+ *   This program is free software: you can redistribute it and/or modify   *
+ *   it under the terms of the GNU General Public License as published by   *
+ *   the Free Software Foundation, either version 3 of the License, or      *
+ *   (at your option) any later version.                                    *
+ *                                                                          *
+ *   This program is distributed in the hope that it will be useful,        *
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of         *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the          *
+ *   GNU General Public License for more details.                           *
+ *                                                                          *
+ *   To view a copy of the GNU General Public License, go to the following  *
+ *   location: <http://www.gnu.org/licenses/>.                              *
+ ****************************************************************************/
+
+#include "../../../inc/MarlinConfigPre.h"
+
+#if ENABLED(EXTENSIBLE_UI)
+
+#include "../ui_api.h"
+
+// To implement a new UI, complete the functions below and
+// read or update Marlin's state using the methods in the
+// UI methods in "../ui_api.h"
+//
+// Although it may be possible to access other state
+// variables from Marlin, using the API here possibly
+// helps ensure future compatibility.
+
+namespace UI {
+  void onStartup() {
+    /* Initialize the display module here. The following
+     * routines are available for access to the GPIO pins:
+     *
+     *   SET_OUTPUT(pin)
+     *   SET_INPUT_PULLUP(pin)
+     *   SET_INPUT(pin)
+     *   WRITE(pin,value)
+     *   READ(pin)
+     */
+  }
+  void onIdle() {}
+  void onPrinterKilled(const char* msg) {}
+  void onMediaInserted();
+  void onMediaError();
+  void onMediaRemoved();
+  void onPlayTone(const uint16_t frequency, const uint16_t duration) {}
+  void onPrintTimerStarted() {}
+  void onPrintTimerPaused() {}
+  void onPrintTimerStopped() {}
+  void onFilamentRunout() {}
+  void onStatusChanged(const char* msg) {}
+  void onStatusChanged(progmem_str msg) {}
+  void onFactoryReset() {}
+  void onLoadSettings() {}
+  void onStoreSettings() {}
+}
+
+#endif // EXTENSIBLE_UI