Fix memory leak when executing vectorized quals

[japinli]

Currently, a VectorColumn structure is created when executing vectorized quals for each tuple on the ExecutorState memory context. However, it will be freed only until execution finishes. This commit changes the memory context to a tuple memory context.

Here are steps to reproduce:

1. Clone tpch-kit.

   git clone https://github.com/gregrahn/tpch-kit.git
   cd tpch-kit/dbgen

2. Compile tpch-kit.
   Make sure the following in Makefie:

   DATABASE = POSTGRESQL
   MACHINE  = LINUX
   WORKLOAD = TPC
   

3. Generate data.

   ./dbgen -s 1
   mkdir s1 && for i in $(ls *.tbl); do sed 's/|$//' $i > s1/${i/tbl/csv}; rm $i; done;

4. Generate load schema and data script.

   cd s1
   echo "CREATE EXTENSION columnar;" > load.sql
   sed 's|);$|) USING columnar;|g' ../dss.ddl >> load.sql
   for csv in $(ls *.csv); do table=$(echo $csv | cut -d. -f1); echo "COPY $table FROM '$PWD/$csv' WITH (FORMAT csv, DELIMITER '|');"; done >> load.sql

5. Initialize the database and load data.

   initdb -D s1data
   pg_ctl -l logfile -D s1data start
   psql -f load.sql postgres

6. Test
   1. Start a new connection using psql;
   2. use top to monitor the memory used by the backend process;
   3. Execute the following query;

      select
        s_name, s_address
      from
        supplier, nation
      where
        s_suppkey in (
          select
            ps_suppkey
          from
            partsupp
          where
            ps_partkey in (
              select
                p_partkey
              from
                part
              where
                p_name like 'khaki%'
            )
            and ps_availqty > (
              select
                0.5 * sum(l_quantity)
              from
                lineitem
              where
                l_partkey = ps_partkey
                and l_suppkey = ps_suppkey
                and l_shipdate >= date '1997-01-01'
                and l_shipdate < date '1997-01-01' + interval '1' year
            )
        )
        and s_nationkey = n_nationkey
        and n_name = 'EGYPT'
      order by
        s_name;

In the top you will see the memory increased and finally cause out of memory.