added proguard settings so that the resulting aar has proguard.txt.

plugins/Android/gradle_build/build.gradle

@@ -13,6 +13,7 @@ android {
         targetSdkVersion 30
         versionCode 1
         versionName "1.0"
+        consumerProguardFiles "consumer-rules.pro"
     }
     buildTypes {
         release {

plugins/Android/gradle_build/consumer-rules.pro

@@ -0,0 +1,3 @@
+-keep class net.gree.unitywebview.** {
+    *;
+}

plugins/Android/gradle_build/proguard-rules.pro

@@ -0,0 +1,21 @@
+# Add project specific ProGuard rules here.
+# You can control the set of applied configuration files using the
+# proguardFiles setting in build.gradle.
+#
+# For more details, see
+#   http://developer.android.com/guide/developing/tools/proguard.html
+
+# If your project uses WebView with JS, uncomment the following
+# and specify the fully qualified class name to the JavaScript interface
+# class:
+#-keepclassmembers class fqcn.of.javascript.interface.for.webview {
+#   public *;
+#}
+
+# Uncomment this to preserve the line number information for
+# debugging stack traces.
+#-keepattributes SourceFile,LineNumberTable
+
+# If you keep the line number information, uncomment this to
+# hide the original source file name.
+#-renamesourcefileattribute SourceFile