Fix CTE recognition after INSERT columns and preserve enclosing indentation

[arnodirlam]

I ran into a couple of indentation problems with CTEs after an INSERT column list: sibling CTEs become progressively indented, and queries inside a PL/pgSQL block can jump back to column zero. This keeps the CTEs and their final query at the enclosing block’s indentation level.

Before (pg_format, default options):

DO $$
BEGIN
    INSERT INTO results (id)
    WITH first_cte AS (
        SELECT
            1 AS id),
        second_cte AS (
            SELECT
                id
            FROM
                first_cte
)
        SELECT
            id
        FROM
            second_cte;
END
$$;

After (pg_format, default options):

DO $$
BEGIN
    INSERT INTO results (id)
    WITH first_cte AS (
        SELECT
            1 AS id
    ),
    second_cte AS (
        SELECT
            id
        FROM
            first_cte
    )
    SELECT
        id
    FROM
        second_cte;
END
$$;

Two existing expected-output files also contained examples of queries losing their enclosing indentation. Their changes reflect the same fix.

I ran prove -l t/ and the larger SQL corpus with perl t/regress_test.pl; both pass. The focused cases also produce the same output when formatted twice.

Thanks for taking a look!