pgsql: Invalidate partitions of table being attached/detached

Invalidate partitions of table being attached/detached

Failing to do that, any direct inserts/updates of those partitions
would fail to enforce the correct constraint, that is, one that
considers the new partition constraint of their parent table.

Backpatch to 10.

Reported by: Hou Zhijie <houzj(dot)fnst(at)fujitsu(dot)com>
Author: Amit Langote <amitlangote09(at)gmail(dot)com>
Author: Álvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>
Reviewed-by: Nitin Jadhav <nitinjadhavpostgres(at)gmail(dot)com>
Reviewed-by: Pavel Borisov <pashkin(dot)elfe(at)gmail(dot)com>

Discussion: https://postgr.es/m/OS3PR01MB5718DA1C4609A25186D1FBF194089%40OS3PR01MB5718.jpnprd01.prod.outlook.com

Branch
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REL_11_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/b703b7d312a75ce3994c82dc71bf04eabb60c49c

Modified Files
--------------
src/backend/commands/tablecmds.c | 35 +++++++++++++++++++++++++++++++
src/test/regress/expected/alter_table.out | 20 ++++++++++++++++++
src/test/regress/sql/alter_table.sql | 19 +++++++++++++++++
3 files changed, 74 insertions(+)