GameActivity PATCH: Rename android_main _rust_glue_entry

The real `android_main` is going to be written in Rust and
android-activity needs to handle its own initialization before calling
the application's `android_main` and so the C/C++ code
calls an intermediate `_rust_glue_entry` function.

Author: rib

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

@@ -234,7 +234,7 @@ static void* android_app_entry(void* param) {
   pthread_cond_broadcast(&android_app->cond);
   pthread_mutex_unlock(&android_app->mutex);
 
-  android_main(android_app);
+  _rust_glue_entry(android_app);
 
   android_app_destroy(android_app);
   return NULL;

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

@@ -481,10 +481,10 @@ void android_app_clear_motion_events(struct android_input_buffer* inputBuffer);
 void android_app_clear_key_events(struct android_input_buffer* inputBuffer);
 
 /**
- * This is the function that application code must implement, representing
- * the main entry to the app.
+ * This is a springboard into the Rust glue layer that wraps calling the
+ * main entry for the app itself.
  */
-extern void android_main(struct android_app* app);
+extern void _rust_glue_entry(struct android_app* app);
 
 /**
  * Set the filter to use when processing key events.