Add PostgreSQL 18 and 19 support to sqlite_fdw

[devrimgunduz]

Fixes all build failures and warnings against PostgreSQL 18 and 19 while preserving full compatibility with PG13 through PG17.

connection.c — PostgreSQL 18 and 19
utils/hsearch.h and utils/tuplestore.h are no longer pulled in
transitively in recent PostgreSQL versions. Add them explicitly and
unconditionally so that HASHCTL, HASH_SEQ_STATUS, hash_create(),
hash_search(), hash_seq_init(), hash_seq_search(), HASH_ELEM,
HASH_BLOBS, HASH_ENTER and tuplestore_putvalues() are visible.

deparse.c — PostgreSQL 19
Three headers dropped from the transitive include chain by PG19's
IWYU cleanup pass; add them explicitly (unconditionally):
catalog/pg_type.h — all *OID and *ARRAYOID type constants
access/htup_details.h — GETSTRUCT()
access/transam.h — FirstGenbkiObjectId

deparse.c — PostgreSQL 18 and 19
PathKey.pk_strategy (int, btree StrategyNumber) was replaced by
pk_cmptype (CompareType) in PG18. The lookup function changed from
get_opfamily_member() to get_opfamily_member_for_cmptype().
BTLessStrategyNumber comparisons use COMPARE_LT instead.
All guarded by #if PG_VERSION_NUM >= 180000. Affects:
sqlite_is_foreign_pathkey() and sqlite_append_order_by_clause().

deparse.c — all versions (warning fix)
Remove dead pindex variable (AttrNumber) from sqlite_deparse_insert()
and sqlite_deparse_update(). The variable was only ever incremented,
never read; SQLite uses unnumbered '?' placeholders.

sqlite_fdw.c — PostgreSQL 19
access/htup_details.h is no longer transitively included for
sqlite_fdw.c in PG19, making SizeofHeapTupleHeader undeclared.
Add the header explicitly (unconditionally; safe on all PG versions).

sqlite_fdw.c — PostgreSQL 19
In PG19, PlanState.instrument changed type from Instrumentation * to
NodeInstrumentation *. The Instrumentation base struct no longer
carries tuplecount (that field moved to NodeInstrumentation). Use
NodeInstrumentation * under #if PG_VERSION_NUM >= 190000 in
sqliteIterateDirectModify(), leaving PG13–18 behaviour unchanged.

sqlite_fdw.c — PostgreSQL 18
create_foreignscan_path(), create_foreign_join_path() and
create_foreign_upper_path() each gained "int disabled_nodes" between
"rows" and "startup_cost". Pass 0 at all ten call sites under a
#if PG_VERSION_NUM >= 180000 guard.
cost_sort() gained "int input_disabled_nodes" between "pathkeys" and
"input_cost". Pass 0 at the one call site under the same guard.
ExplainPropertyText(), ExplainPropertyInteger() and the ExplainState
struct were split into commands/explain_format.h and
commands/explain_state.h; include both for PG18+.

sqlite_fdw.c — all versions (warning fix)
Remove dead variable i (int) from sqliteExecForeignUpdate(); it was
only incremented, never read.

sqlite_query.c — PostgreSQL 19
VARDATA() and SET_VARSIZE() became strict-typed static inline
functions in PG19 requiring a pointer argument. Wrap the raw Datum
value_datum with DatumGetPointer() at both call sites in
sqlite_convert_to_pg(). DatumGetPointer() is a safe portable cast
on all supported PG versions.

Coded by Claude, tested by me.

Per pgdg-packaging/pgdg-rpms#213