Bug: pg_get_viewdef() fails on GRAPH_TABLE views with lateral column references

Hi hackers,

pg_get_viewdef() fails with ERROR: bogus varlevelsup: 0 offset 0 for any
view containing a GRAPH_TABLE whose COLUMNS clause references an outer
(lateral)
table. This also breaks pg_dump and \d+ for any database containing such a
view.

Repro:

CREATE TABLE vtab (id int PRIMARY KEY, name text);
CREATE TABLE etab (eid int PRIMARY KEY,
    src int REFERENCES vtab(id), dst int REFERENCES vtab(id));
CREATE PROPERTY GRAPH g1
    VERTEX TABLES (vtab)
    EDGE TABLES (etab KEY (eid)
        SOURCE KEY (src) REFERENCES vtab(id)
        DESTINATION KEY (dst) REFERENCES vtab(id));
CREATE TABLE outer_t (val int);

CREATE VIEW v AS
  SELECT * FROM outer_t,
    GRAPH_TABLE (g1 MATCH (a IS vtab)
      COLUMNS (a.name AS src_name, outer_t.val AS oval));

pg_dump -d foo -p 5433
pg_dump: error: query failed: ERROR:  bogus varlevelsup: 0 offset 0
pg_dump: detail: Query was: SELECT
pg_catalog.pg_get_viewdef('173849'::pg_catalog.oid) AS viewdef

Problem:
deparse_context context variable declared in the case RTE_GRAPH_TABLE
shadows the function's
deparse_context *context parameter. The zeroed struct has namespaces = NIL,
so when get_rule_expr()
reaches a Var node, get_variable() sees list_length(context->namespaces) ==
0 and raises the error. Property
references are fine because GraphPropertyRef deparsing never touches
namespaces.

Fix:
Remove the shadowing local variable and pass the outer context pointer to
get_rule_expr(). Attached a patch
with a fix, additionally added a test.

Thanks,
Satya