Open source stub APK loader

Close #3537

stub/src/main/java/com/topjohnwu/magisk/DelegateApplication.java

@@ -0,0 +1,41 @@
+package com.topjohnwu.magisk;
+
+import android.app.Application;
+import android.content.Context;
+import android.content.ContextWrapper;
+import android.content.res.Configuration;
+import android.os.Build;
+
+import java.lang.reflect.Method;
+
+public class DelegateApplication extends Application {
+
+    private Application delegate;
+    static boolean dynLoad = false;
+
+    @Override
+    protected void attachBaseContext(Context base) {
+        super.attachBaseContext(base);
+
+        // Only dynamic load full APK if hidden and possible
+        dynLoad = Build.VERSION.SDK_INT >= 28 &&
+                !base.getPackageName().equals(BuildConfig.APPLICATION_ID);
+        if (!dynLoad)
+            return;
+
+        delegate = InjectAPK.setup(this);
+        if (delegate != null) try {
+            // Call attachBaseContext without ContextImpl to show it is being wrapped
+            Method m = ContextWrapper.class.getDeclaredMethod("attachBaseContext", Context.class);
+            m.setAccessible(true);
+            m.invoke(delegate, this);
+        } catch (Exception ignored) { /* Impossible */ }
+    }
+
+    @Override
+    public void onConfigurationChanged(Configuration newConfig) {
+        super.onConfigurationChanged(newConfig);
+        if (delegate != null)
+            delegate.onConfigurationChanged(newConfig);
+    }
+}