GameActivity PATCH: Expose TextEvent and input method state

This also adds `InputEvent::TextEvent` for notifying applications of IME
state changes as well as explicit getter/setter APIs for tracking IME
selection + compose region state. (only supported with GameActivity)

Fixes: #18

Author: rib

android-activity/game-activity-csrc/game-activity/native_app_glue/android_native_app_glue.c

@@ -680,6 +680,7 @@ static void onTextInputEvent(GameActivity* activity,
   pthread_mutex_lock(&android_app->mutex);
   if (!android_app->destroyed) {
     android_app->textInputState = 1;
+    notifyInput(android_app);
   }
   pthread_mutex_unlock(&android_app->mutex);
 }