Update feature column migration guide with hashed crossing layer

PiperOrigin-RevId: 431508229

Author: mattdangerw

site/en/guide/migrate/migrating_feature_columns.ipynb

@@ -919,7 +919,7 @@
         "  </tr>\n",
         "  <tr>\n",
         "    <td>`feature_column.crossed_column`</td>\n",
-        "    <td>Not implemented.</td>\n",
+        "    <td>`layers.experimental.preprocessing.HashedCrossing`</td>\n",
         "  </tr>\n",
         "  <tr>\n",
         "    <td>`feature_column.embedding_column`</td>\n",