[Patch]Add Graph* node support to expression_tree_mutator

Hi hackers,

expression_tree_mutator_impl() was missing case handlers for
T_GraphPattern, T_GraphElementPattern, and T_GraphPropertyRef.
The corresponding expression_tree_walker_impl() already handled
all three node types, but the mutator did not, causing an
"unrecognized node type: 106" error whenever a GRAPH_TABLE
subquery appeared in a HAVING clause.

SELECT 1 FROM hv GROUP BY id
HAVING (SELECT COUNT(*) FROM GRAPH_TABLE(gh MATCH (a) COLUMNS (a.id AS x)))
> 0;
SET
ERROR: unrecognized node type: 106

Attached a patch to address this.

Thanks,
Satya