pgsql: Revert support for ALTER TABLE ... MERGE/SPLIT PARTITION(S) comm

Revert support for ALTER TABLE ... MERGE/SPLIT PARTITION(S) commands

This commit reverts f2e4cc4279 and 4b3d173629, and the subsequent fixes and
improvements c5ae07a90a, 713e553e32, 52e629be95, ecb2508aaf, 9354896920,
971017c495, 83df16f1fa, e64a9ba2b4, ff8bec8c46, cdae794af3, 57f19774d6, and
881033ae8b. d8af730100 and 0392fb900e cancelled each other out and are not
reverted separately.

The feature is reverted due to multiple design issues which are too late to
address in this release cycle.

Discussion: https://postgr.es/m/CAN4CZFNCU%3Dt09M%3D%2Br2t9hHLJuujdM4oQ8hCK_Sx-GpfiwMAicw%40mail.gmail.com

Branch
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REL_19_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/3e8bcc8644feaa9ca1cc954197b6994817af4290

Modified Files
--------------
doc/src/sgml/ddl.sgml | 38 -
doc/src/sgml/ref/alter_table.sgml | 272 +--
src/backend/catalog/dependency.c | 54 +-
src/backend/catalog/pg_constraint.c | 2 +-
src/backend/commands/tablecmds.c | 1649 +-----------------
src/backend/parser/gram.y | 60 +-
src/backend/parser/parse_utilcmd.c | 338 +---
src/backend/partitioning/partbounds.c | 1054 ------------
src/bin/psql/tab-complete.in.c | 18 +-
src/include/catalog/dependency.h | 2 -
src/include/nodes/parsenodes.h | 34 +-
src/include/parser/kwlist.h | 2 -
src/include/partitioning/partbounds.h | 10 -
src/test/isolation/expected/partition-merge.out | 243 ---
src/test/isolation/expected/partition-split.out | 230 ---
src/test/isolation/isolation_schedule | 2 -
src/test/isolation/specs/partition-merge.spec | 62 -
src/test/isolation/specs/partition-split.spec | 62 -
.../test_ddl_deparse/expected/alter_table.out | 10 -
.../modules/test_ddl_deparse/sql/alter_table.sql | 7 -
.../modules/test_ddl_deparse/test_ddl_deparse.c | 6 -
.../test_extensions/expected/test_extdepend.out | 120 --
.../modules/test_extensions/sql/test_extdepend.sql | 104 --
src/test/regress/expected/partition_merge.out | 1174 -------------
src/test/regress/expected/partition_split.out | 1758 --------------------
src/test/regress/parallel_schedule | 2 +-
src/test/regress/sql/partition_merge.sql | 846 ----------
src/test/regress/sql/partition_split.sql | 1263 --------------
src/tools/pgindent/typedefs.list | 3 -
29 files changed, 46 insertions(+), 9379 deletions(-)