Dynamic load updated APK for patching

Magisk Manager sometimes updates the code for patching the APK due to several changes.
When an old manager tries to patch an updated APK using its internal methods, it is
sometimes incomplete, or simply won't work at all.

This commit exposes an API that can be dynamically loaded from an old app to invoke the
updated patchAPK method from the downloaded new APK.

app/src/full/java/a/a.java

@@ -1,10 +1,13 @@
 package a;
 
 import com.topjohnwu.core.utils.BootSigner;
+import com.topjohnwu.magisk.utils.PatchAPK;
 
 import androidx.annotation.Keep;
 
 @Keep
 public class a extends BootSigner {
-    /* stub */
+    public static boolean patchAPK(String in, String out, String pkg) {
+        return PatchAPK.patch(in, out, pkg);
+    }
 }