Marking dictionary activity as visibleToInstantApps

Without this change, prompts to the user to add a word entered into
one of the text fields within an instant app would result in a crash.

Change-Id: I98c9dd21d4fbf6f65c519b7e34bcc11f43b6a92e
Fixes: 77273200
Test: manual - trigger add word launch from instant app

AndroidManifest.xml

@@ -700,6 +700,7 @@
         </activity>
 
         <activity android:name=".inputmethod.UserDictionaryAddWordActivity"
+                  android:visibleToInstantApps="true"
                   android:label="@string/user_dict_settings_title"
                   android:theme="@*android:style/Theme.DeviceDefault.Settings.Dialog.NoActionBar"
                   android:windowSoftInputMode="stateVisible"