fix: Columns not visible when using a VLE. (#609)

[emotionbug]

No description provided.

[yjy44]

Please explain briefly about the continuation of the pathout and the VLE.

[emotionbug]

There are two issues found in the issue in #609.

First thing, because the target of a Joinlist is not visible, some statement can't perform the logic of how to join with it.

agensgraph/src/backend/parser/parse_graph.c

Line 1918 in 91ff58c

addNSItemToJoinlist(pstate, nsitem, true);

this resolves the errors, but ruins the results of the join with the unnamed VLE.

Second thing, problem is that in statements like the one in this problem, AgensGraph is forced to treat joins as paths.
however, except for types like ShortestPath, if the name of the path does not exist, it is not treated as a path.
this leads to a deviation from the expected behavior and results in an invalid join.