Fix indentation of procedural IF EXISTS blocks - #413

While formatting a PL/pgSQL block, I noticed that the body of IF EXISTS / IF NOT EXISTS was aligned with the IF, and END IF moved outside the enclosing block. This fixes the indentation so the branches are easier to follow.

Before (pg_format, default options):

DO $$
BEGIN
    IF NOT EXISTS (
        SELECT
            1
        FROM
            widgets
        WHERE
            id = 1
            AND enabled) THEN
    EXECUTE $sql$select 1;$sql$;
END IF;
END
$$;

After (pg_format, default options):

DO $$
BEGIN
    IF NOT EXISTS (
        SELECT
            1
        FROM
            widgets
        WHERE
            id = 1
            AND enabled) THEN
        EXECUTE $sql$select 1;$sql$;
    END IF;
END
$$;

The existing opr_sanity.sql expected output contained the same indentation issue, so I’ve corrected that too.

I ran prove -l t/ and the larger SQL corpus with perl t/regress_test.pl; both pass. I also checked that formatting the new example twice produces the same output.

Thanks for maintaining pgFormatter!