pgsql: Support MERGE into updatable views.

Support MERGE into updatable views.

This allows the target relation of MERGE to be an auto-updatable or
trigger-updatable view, and includes support for WITH CHECK OPTION,
security barrier views, and security invoker views.

A trigger-updatable view must have INSTEAD OF triggers for every type
of action (INSERT, UPDATE, and DELETE) mentioned in the MERGE command.
An auto-updatable view must not have any INSTEAD OF triggers. Mixing
auto-update and trigger-update actions (i.e., having a partial set of
INSTEAD OF triggers) is not supported.

Rule-updatable views are also not supported, since there is no
rewriter support for non-SELECT rules with MERGE operations.

Dean Rasheed, reviewed by Jian He and Alvaro Herrera.

Discussion: https://postgr.es/m/CAEZATCVcB1g0nmxuEc-A+gGB0HnfcGQNGYH7gS=7rq0u0zOBXA@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/5f2e179bd31e5f5803005101eb12a8d7bf8db8f3

Modified Files
--------------
doc/src/sgml/ref/create_view.sgml | 42 +-
doc/src/sgml/ref/merge.sgml | 22 +-
doc/src/sgml/rules.sgml | 40 +-
src/backend/commands/copyfrom.c | 2 +-
src/backend/executor/execMain.c | 51 +--
src/backend/executor/execPartition.c | 4 +-
src/backend/executor/nodeModifyTable.c | 138 +++++--
src/backend/optimizer/prep/prepjointree.c | 20 +-
src/backend/optimizer/util/appendinfo.c | 3 +-
src/backend/parser/parse_merge.c | 21 +-
src/backend/rewrite/rewriteHandler.c | 403 +++++++++++++------
src/backend/rewrite/rewriteManip.c | 20 +-
src/bin/psql/tab-complete.c | 1 +
src/include/catalog/catversion.h | 2 +-
src/include/executor/executor.h | 3 +-
src/include/nodes/parsenodes.h | 8 +
src/include/rewrite/rewriteHandler.h | 6 +
src/test/regress/expected/merge.out | 10 -
src/test/regress/expected/rules.out | 12 +
src/test/regress/expected/updatable_views.out | 553 +++++++++++++++++++++++++-
src/test/regress/sql/merge.sql | 9 -
src/test/regress/sql/rules.sql | 13 +
src/test/regress/sql/updatable_views.sql | 285 ++++++++++++-
23 files changed, 1380 insertions(+), 288 deletions(-)