InkHUD: Allow non-system applets to subscribe to input events (#9514)

* Allow inkhud user applets to consume inputs with opt-in system
Adds a way for applets to subscribe to input events while keeping it off
by default to preserve compatibility and expected behaviours. Adds
example for use as well.
* Add check for nullptr on getActiveApplet uses
* Remove redundant includes
* Move subscribedInputs to protected
* More consistent naming scheme

src/graphics/niche/InkHUD/Applets/Examples/UserAppletInputExample/UserAppletInputExample.cpp

@@ -0,0 +1,79 @@
+#ifdef MESHTASTIC_INCLUDE_INKHUD
+#include "./UserAppletInputExample.h"
+
+using namespace NicheGraphics;
+
+void InkHUD::UserAppletInputExampleApplet::onActivate()
+{
+    setGrabbed(false);
+}
+
+void InkHUD::UserAppletInputExampleApplet::onRender(bool full)
+{
+    drawHeader("Input Example");
+    uint16_t headerHeight = getHeaderHeight();
+
+    std::string buttonName;
+    if (settings->joystick.enabled)
+        buttonName = "joystick center button";
+    else
+        buttonName = "user button";
+
+    std::string additional = " | Control is grabbed, long press " + buttonName + " to release controls";
+    if (!isGrabbed)
+        additional = " | Control is released, long press " + buttonName + " to grab controls";
+
+    printWrapped(0, headerHeight, width(), "Last button: " + lastInput + additional);
+}
+
+void InkHUD::UserAppletInputExampleApplet::setGrabbed(bool grabbed)
+{
+    isGrabbed = grabbed;
+    setInputsSubscribed(BUTTON_SHORT | EXIT_SHORT | EXIT_LONG | NAV_UP | NAV_DOWN | NAV_LEFT | NAV_RIGHT,
+                        grabbed);           // Enables/disables grabbing all inputs
+    setInputsSubscribed(BUTTON_LONG, true); // Always grab this input
+}
+
+void InkHUD::UserAppletInputExampleApplet::onButtonShortPress()
+{
+    lastInput = "BUTTON_SHORT";
+    requestUpdate();
+}
+void InkHUD::UserAppletInputExampleApplet::onButtonLongPress()
+{
+    lastInput = "BUTTON_LONG";
+    setGrabbed(!isGrabbed);
+    requestUpdate();
+}
+void InkHUD::UserAppletInputExampleApplet::onExitShort()
+{
+    lastInput = "EXIT_SHORT";
+    requestUpdate();
+}
+void InkHUD::UserAppletInputExampleApplet::onExitLong()
+{
+    lastInput = "EXIT_LONG";
+    requestUpdate();
+}
+void InkHUD::UserAppletInputExampleApplet::onNavUp()
+{
+    lastInput = "NAV_UP";
+    requestUpdate();
+}
+void InkHUD::UserAppletInputExampleApplet::onNavDown()
+{
+    lastInput = "NAV_DOWN";
+    requestUpdate();
+}
+void InkHUD::UserAppletInputExampleApplet::onNavLeft()
+{
+    lastInput = "NAV_LEFT";
+    requestUpdate();
+}
+void InkHUD::UserAppletInputExampleApplet::onNavRight()
+{
+    lastInput = "NAV_RIGHT";
+    requestUpdate();
+}
+
+#endif