pgsql: Add some regression tests for missing DDL patterns

Add some regression tests for missing DDL patterns

The following commands gain increased coverage for some of the errors
they can trigger:
- ALTER TABLE .. ALTER COLUMN
- CREATE DOMAIN
- CREATE TYPE (LIKE)

This has come up while discussing the possibility to add more
information about the location of the error in such queries, and it
is useful on its own as there was no coverage until now for the
patterns added in this commit.

Author: Jian He, Kirill Reshke
Reviewed-By: Álvaro Herrera, Michael Paquier
Discussion: https://postgr.es/m/CALdSSPhqfvKbDwqJaY=yEePi_aq61GmMpW88i6ZH7CMG_2Z4Cg@mail.gmail.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/0172b4c9449e92a3988f669d9e7e9000454d16ce

Modified Files
--------------
src/test/regress/expected/alter_table.out | 7 +++++++
src/test/regress/expected/domain.out | 27 +++++++++++++++++++++++++++
src/test/regress/expected/float8.out | 2 ++
src/test/regress/expected/identity.out | 2 ++
src/test/regress/sql/alter_table.sql | 5 +++++
src/test/regress/sql/domain.sql | 14 ++++++++++++++
src/test/regress/sql/float8.sql | 1 +
src/test/regress/sql/identity.sql | 1 +
8 files changed, 59 insertions(+)