feat: improve pgsql grammar and add unit tests(#201)

* feat(pgsql: upgrade keywords and refresh them to parser file): pgsql

* feat(pgsql: check create table's syntax): pgsql

* feat(pgsql: check and update drop syntax): pgsql: check and update drop syntax

* feat: pgsql: check create's sql syntax and update g4 file

* feat: pgsql:complete other's sql and syntax except select, insert, drop

* feat: pgsql: update create, delete, insert, select, update and others' syntax

* test: pgsql: update alter's sql

* feat: pgsql: update syntax g4 file

* feat: pgsql: upgrade keywords to without '_P' in lexer and parser file

* docs: pgsql: update copyright and Reference of parser and lexer

---------

Co-authored-by: zhaoge <>

Author: Cythia828