add post_notification permission to manifest

so the package can send notifications on T+

Bug: 194833441
Change-Id: Iafb56ebd788f1dcd98320dc6c250ca8f585fcab3

tools/EditTextVariations/AndroidManifest.xml

@@ -21,6 +21,7 @@
     <supports-screens android:resizeable="true"/>
     <uses-sdk android:targetSdkVersion="27"
          android:minSdkVersion="11"/>
+    <uses-permission android:name="android.permission.POST_NOTIFICATIONS"/>
     <application android:icon="@drawable/ic_launcher"
          android:label="@string/app_name"
          android:allowBackup="false">