pgsql: Fix virtual generated column type checking for ALTER TABLE

Fix virtual generated column type checking for ALTER TABLE

Virtual generated columns have some special checks in
CheckAttributeType(), mainly to check that domains are not used.  But
this check was only applied during CREATE TABLE, not during ALTER
TABLE.  This fixes that.

Reported-by: jian he <jian.universality@gmail.com>
Discussion: https://www.postgresql.org/message-id/CACJufxE0KHR__-h=zHXbhSNZXMMs4LYo4-dbj8H3YoStYBok1Q@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/49fe1c83ecf3474776ea9d0db47ae5644d29b67b

Modified Files
--------------
src/backend/commands/tablecmds.c                | 4 ++--
src/test/regress/expected/generated_virtual.out | 6 ++++++
src/test/regress/sql/generated_virtual.sql      | 5 +++++
3 files changed, 13 insertions(+), 2 deletions(-)