refactor: Add keep rules for java types (#949)

We're working to narrow down our consumer rules in
RevenueCat/purchases-android#3557. However, this
makes it not find our code anymore in Unity when minifying since nothing
is directly referencing the Java types from Unity. This adds some Keep
annotations that from my tests avoid the issue. This does mean we will
need to remember to mark all java types as `@Keep` but it was easier
than trying to add proguard rules to be used by our customers when
importing our plugins.

Note this won't do anything until the purchases-android changes actually
get merged

Author: tonidero

RevenueCat/Plugins/Android/PurchasesWrapper.java

@@ -2,6 +2,7 @@
 
 import android.util.Log;
 
+import androidx.annotation.Keep;
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 
@@ -37,6 +38,7 @@
 
 import kotlin.Unit;
 
+@Keep
 public class PurchasesWrapper {
     private static final String RECEIVE_STOREFRONT = "_receiveStorefront";
     private static final String RECEIVE_PRODUCTS = "_receiveProducts";

RevenueCatUI/Plugins/Android/RevenueCatUI.androidlib/src/main/java/com/revenuecat/purchasesunity/ui/CustomerCenterTrampolineActivity.java

@@ -7,6 +7,7 @@
 
 import androidx.activity.ComponentActivity;
 import androidx.activity.result.ActivityResultLauncher;
+import androidx.annotation.Keep;
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 
@@ -20,6 +21,7 @@
 
 import kotlin.Unit;
 
+@Keep
 public class CustomerCenterTrampolineActivity extends ComponentActivity {
     private static final String TAG = "PurchasesUnity";
 

RevenueCatUI/Plugins/Android/RevenueCatUI.androidlib/src/main/java/com/revenuecat/purchasesunity/ui/PaywallViewPresenter.java

@@ -19,6 +19,7 @@
 import androidx.activity.OnBackPressedDispatcher;
 import androidx.activity.OnBackPressedDispatcherOwner;
 import androidx.activity.ViewTreeOnBackPressedDispatcherOwner;
+import androidx.annotation.Keep;
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import androidx.core.graphics.Insets;
@@ -52,6 +53,7 @@
 
 import kotlin.Unit;
 
+@Keep
 public class PaywallViewPresenter {
 
     private static final String TAG = "PurchasesUnity";

RevenueCatUI/Plugins/Android/RevenueCatUI.androidlib/src/main/java/com/revenuecat/purchasesunity/ui/RevenueCatUI.java

@@ -3,18 +3,23 @@
 import android.app.Activity;
 import android.util.Log;
 
+import androidx.annotation.Keep;
 import androidx.annotation.Nullable;
 
 import com.revenuecat.purchases.hybridcommon.ui.HybridPurchaseLogicBridge;
 
+@Keep
 public class RevenueCatUI {
+    @Keep
     public interface PaywallCallbacks { void onPaywallResult(String result); }
 
+    @Keep
     public interface PurchaseLogicCallbacks {
         void onPerformPurchase(String requestId, String packageJson);
         void onPerformRestore(String requestId);
     }
 
+    @Keep
     public interface CustomerCenterCallbacks {
         void onCustomerCenterDismissed();
         void onCustomerCenterError();