[webview_flutter] (Trivial) Add V2 warnings

packages/webview_flutter/android/src/main/java/io/flutter/plugins/webviewflutter/WebViewFlutterPlugin.java

@@ -26,6 +26,11 @@ public class WebViewFlutterPlugin implements FlutterPlugin {
    * Add an instance of this to {@link io.flutter.embedding.engine.plugins.PluginRegistry} to
    * register it.
    *
+   * <p>THIS PLUGIN CODE PATH DEPENDS ON A NEWER VERSION OF FLUTTER THAN THE ONE DEFINED IN THE
+   * PUBSPEC.YAML. Text input will fail on some Android devices unless this is used with at least
+   * flutter/flutter@1d4d63ace1f801a022ea9ec737bf8c15395588b9. Use the V1 embedding with {@link
+   * #registerWith(Registrar)} to use this plugin with older Flutter versions.
+   *
    * <p>Registration should eventually be handled automatically by v2 of the
    * GeneratedPluginRegistrant. https://github.com/flutter/flutter/issues/42694
    */

packages/webview_flutter/example/android/app/src/main/java/io/flutter/plugins/webviewflutterexample/MainActivity.java

@@ -8,6 +8,14 @@
 import io.flutter.embedding.engine.FlutterEngine;
 import io.flutter.plugins.webviewflutter.WebViewFlutterPlugin;
 
+/**
+ * THIS PLUGIN CODE PATH DEPENDS ON A NEWER VERSION OF FLUTTER THAN THE ONE DEFINED IN THE
+ * PUBSPEC.YAML. Text input will fail on some Android devices unless this is used with at least
+ * flutter/flutter@1d4d63ace1f801a022ea9ec737bf8c15395588b9.
+ *
+ * <p>Use the V1 embedding as seen in {@link EmbeddingV1Activity} to use this plugin on older
+ * Flutter versions.
+ */
 public class MainActivity extends FlutterActivity {
   // TODO(mklim): Remove this once v2 of GeneratedPluginRegistrant rolls to stable. https://github.com/flutter/flutter/issues/42694
   @Override