Feature: Import PostgreSQL 16 BETA1 new parser.

Feature: Import PostgreSQL 16 BETA1 new parser.

Major changes of PostgreSQL 16 parser include:

- Add new option DEFAULT to COPY FROM

  COPY ... FROM stdin WITH (default 'xx');

- Allow the STORAGE type to be specified by CREATE TABLE

  CREATE TABLE t1 (
     c1 VARCHAR(10) STORAGE PLAIN,
     c2 TEXT STORAGE EXTENDED
  );

- Add EXPLAIN option GENERIC_PLAN to display the generic plan for a parameterized query

  EXPLAIN (GENERIC_PLAN) SELECT ...;

- Allow subqueries in the FROM clause to omit aliases

  SELECT COUNT(*) FROM (SELECT ... FROM ...);

- Add SQL/JSON constructors

- Add VACUUM options
  SKIP_DATABASE_STATS, ONLY_DATABASE_STATS to skip or update all frozen statistics
  PROCESS_MAIN to only process TOAST tables

  VACUUM (SKIP_DATABASE_STATS);
  VACUUM (PROCESS_MAIN FALSE) t1 ;