Bug: Missing collation assignment for GRAPH_TABLE COLUMNS expressions

Hi hackers,

GRAPH_TABLE COLUMNS expressions that involve collation-dependent functions
or operators fail with:

ERROR: could not determine which collation to use for upper() function
HINT: Use the COLLATE clause to set the collation explicitly.

Setup:

CREATE TABLE vtx (id int PRIMARY KEY, name text);
CREATE TABLE edg (id int PRIMARY KEY,
src int REFERENCES vtx(id),
dst int REFERENCES vtx(id));
INSERT INTO vtx VALUES (1,'Alice'),(2,'Bob'),(3,'Carol');
INSERT INTO edg VALUES (1,1,2),(2,2,3);

CREATE PROPERTY GRAPH g
VERTEX TABLES (vtx KEY (id))
EDGE TABLES (edg KEY (id)
SOURCE KEY (src) REFERENCES vtx (id)
DESTINATION KEY (dst) REFERENCES vtx (id));

postgres=# SELECT * FROM GRAPH_TABLE (g
MATCH (a IS vtx)-[e IS edg]->(b IS vtx) COLUMNS (upper(a.name) AS
src_upper));
ERROR: could not determine which collation to use for upper() function
HINT: Use the COLLATE clause to set the collation explicitly.

In transformRangeGraphTable(), the COLUMNS transformation loop calls
transformExpr()
on each column expression but omits the subsequent assign_expr_collations()
call. Both
WHERE clause transformation sites in parse_graphtable.c correctly include
it.

Attached a patch to fix this.

Thanks,
Satya