Add signals and a check function for Android service connectivity.

- Add a iap_connect and iap_disconnect events for android platform.
- Add isConnected() function returning true if its connected to android service, false otherwise

(cherry picked from commit 546b48813f)

platform/android/java/src/org/godotengine/godot/GodotPaymentV3.java

@@ -67,7 +67,7 @@ public class GodotPaymentV3 extends Godot.SingletonBase {
 
 	public GodotPaymentV3(Activity p_activity) {
 
-		registerClass("GodotPayments", new String[] { "purchase", "setPurchaseCallbackId", "setPurchaseValidationUrlPrefix", "setTransactionId", "getSignature", "consumeUnconsumedPurchases", "requestPurchased", "setAutoConsume", "consume", "querySkuDetails" });
+		registerClass("GodotPayments", new String[] { "purchase", "setPurchaseCallbackId", "setPurchaseValidationUrlPrefix", "setTransactionId", "getSignature", "consumeUnconsumedPurchases", "requestPurchased", "setAutoConsume", "consume", "querySkuDetails", "isConnected" });
 		activity = (Godot)p_activity;
 		mPaymentManager = activity.getPaymentsManager();
 		mPaymentManager.setBaseSingleton(this);
@@ -164,6 +164,19 @@ public class GodotPaymentV3 extends Godot.SingletonBase {
 		GodotLib.calldeferred(purchaseCallbackId, "has_purchased", new Object[] { receipt, signature, sku });
 	}
 
+	public void callbackDisconnected() {
+		GodotLib.calldeferred(purchaseCallbackId, "iap_disconnected", new Object[]{});
+	}
+
+	public void callbackConnected() {
+		GodotLib.calldeferred(purchaseCallbackId, "iap_connected", new Object[]{});
+	}
+
+	// true if connected, false otherwise
+	public boolean isConnected() {
+		return mPaymentManager.isConnected();
+	}
+
 	// consume item automatically after purchase. default is true.
 	public void setAutoConsume(boolean autoConsume) {
 		mPaymentManager.setAutoConsume(autoConsume);

platform/android/java/src/org/godotengine/godot/payments/PaymentsManager.java

@@ -93,11 +93,21 @@ public class PaymentsManager {
 		@Override
 		public void onServiceDisconnected(ComponentName name) {
 			mService = null;
+
+			// At this stage, godotPaymentV3 might not have been initialized yet.
+			if (godotPaymentV3 != null) {
+				godotPaymentV3.callbackDisconnected();
+			}
 		}
 
 		@Override
 		public void onServiceConnected(ComponentName name, IBinder service) {
 			mService = IInAppBillingService.Stub.asInterface(service);
+
+			// At this stage, godotPaymentV3 might not have been initialized yet.
+			if (godotPaymentV3 != null) {
+				godotPaymentV3.callbackConnected();
+			}
 		}
 	};
 
@@ -123,6 +133,10 @@ public class PaymentsManager {
 				.purchase(sku, transactionId);
 	}
 
+	public boolean isConnected() {
+		return mService != null;
+	}
+
 	public void consumeUnconsumedPurchases() {
 		new ReleaseAllConsumablesTask(mService, activity) {