fix(optimizer): postgres qualify GENERATE_SERIES and table as column reference

[geooo109]

Fixes #6358

This PR fixes the qualification of GENERATE_SERIES and table as column.

GENERATE_SERIES

SELECT * FROM GENERATE_SERIES(1, 2);
 generate_series 
-----------------
               1
               2
(2 rows)

In postgres GENERATE_SERIES creates a column generate_series, thus in order to safely qualify this we have the two following cases:

1. Without alias: we just create an alias on optimization time and use the default generate_series column:

SELECT generate_series FROM GENERATE_SERIES(1,2); => SELECT generate_series FROM GENERATE_SERIES(1, 2) AS _q_0(generate_series);

2. With alias: we wrap it with a generated alias from the optimizer:

SELECT g FROM GENERATE_SERIES(1,2) AS g; => SELECT g FROM GENERATE_SERIES(1, 2) AS _q_0(g);

Table projection
postgres supports:

SELECT t FROM t;

The type of t is record, which is an abstract type. We treat this case as the bigquerry table-column reference.

[georgesittas]

I don't feel great about this change.

I think there are other dialects besides postgres, and also other functions besides generate_series, that are "special", in the sense that they generate a single column that you can project directly. Manually handling these doesn't really scale, so we should find a cleaner way to support this case.

Since we now iterate over all tables in L161, perhaps we can handle these cases there.

[geooo109]

Yeap, I had the same intuition when I was implementing it, will make it more generic and re-push.