pgsql: Allow ALTER VIEW command to rename the column in the view.

Allow ALTER VIEW command to rename the column in the view.

ALTER TABLE RENAME COLUMN command always can be used to rename the column
in the view, but it's reasonable to add that syntax to ALTER VIEW too.

Author: Fujii Masao
Reviewed-by: Ibrar Ahmed, Yu Kimura
Discussion: https://postgr.es/m/CAHGQGwHoQMD3b-MqTLcp1MgdhCpOKU7QNRwjFooT4_d+ti5v6g@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/30840c92ac0c4073fb7bc8222317630571b8cf25

Modified Files
--------------
doc/src/sgml/ref/alter_view.sgml          | 19 +++++++++++++++++++
src/backend/commands/view.c               |  3 ++-
src/backend/parser/gram.y                 | 22 ++++++++++++++++++++++
src/bin/psql/tab-complete.c               | 14 +++++++++++++-
src/test/regress/expected/create_view.out | 27 ++++++++++++++++++++++++++-
src/test/regress/sql/create_view.sql      |  6 ++++++
6 files changed, 88 insertions(+), 3 deletions(-)