SqlSmith: Enable gen subqueries. Finding the bug and solving it

[marvenlee2486]

TODO list

• Resolve Bug: 1) feat(sqlsmith): enable sub-query generation #4216
• Resolve Bug: 2)

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I am debugging on the subqueries, in my knowledge there are many types of subquery
Scalar, Row subqueries (in clauses), Table subqueries
And there is Uncorrelated subquries, and Correlated Subquery.

Currently, sqlsmith seems to only support table subqueries that are used in FROM statement. (I dun think the case where x in select(...) is being implemented (I can think of implementing this in later time).

And there is a few bug I notice, (Still need more debugging)

1. We cannot

Select * 
From t1, (select t1.x) 

but we can

select *
from t1,
where t1.x in (select t1.x)

Current SqlSmith does not generate the 2nd one. However, it wrongly generated the 1st one.

2. Another one is regarding a bug in the correlated issue, Internal Error: correlated InputRef having some issue when group by table outside the subquery/ #3934

There may be more, let me fix the 1st one first.