throw warning when incompatible com.android.application plugin is used

see #1909

packages/stripe_android/android/build.gradle

@@ -65,3 +65,12 @@ dependencies {
     // Users need to declare this dependency on their own, otherwise all methods are a no-op
     compileOnly 'com.stripe:stripe-android-issuing-push-provisioning:1.1.0'
 }
+
+afterEvaluate {
+    // check version of com.android.application - fail if 8.0.0 or higher
+    def androidPluginVersion = com.android.Version.ANDROID_GRADLE_PLUGIN_VERSION
+    print("android plugin version: " + androidPluginVersion)
+    if (androidPluginVersion >= '8.0.0') {
+        throw new GradleException("flutter_stripe: Stripe Android SDK requires com.android.application plugin lower than 8.0.0.\nSee https://github.com/flutter-stripe/flutter_stripe/issues/1909\n")
+    }
+}