prevent R8 shrinking from removing Tor’s private JNI fields

packages/flutter_tor/android/build.gradle

@@ -56,6 +56,7 @@ android {
 
     defaultConfig {
         minSdk = 24
+        consumerProguardFiles("consumer-rules.pro")
     }
 
     dependencies {

packages/flutter_tor/android/consumer-rules.pro

@@ -0,0 +1,11 @@
+####################################################################################################
+# tor-android JNI
+####################################################################################################
+
+# libtor accesses these fields and native methods by their Java names/signatures.
+# Release R8 shrinking can otherwise remove private fields that are only used from JNI.
+-keep class org.torproject.jni.TorService {
+    long torConfiguration;
+    int torControlFd;
+    native <methods>;
+}