[SPARK-13755] Escape quotes in SQL plan visualization node labels

When generating Graphviz DOT files in the SQL query visualization we need to escape double-quotes inside node labels. This is a followup to #11309, which fixed a similar graph in Spark Core's DAG visualization.

Author: Josh Rosen <joshrosen@databricks.com>

Closes #11587 from JoshRosen/graphviz-escaping.