Add PostgreSQL 19 compatibility

[adeshthack]

Description

Summary

pg_stat_monitor fails to build against PostgreSQL 19 (19devel) due to several API changes. The
current CI matrix covers PG 14-18 only.

Build Failures

The following PG19 API changes break compilation:

1. planner_hook signature change — now takes an additional ExplainState *es parameter
2. QueryDesc->totaltime renamed to QueryDesc->query_instr — PG19 manages the
   InstrStart/InstrStop lifecycle automatically via query_instr_options
3. LWLockNewTrancheId() now requires a name argument
4. ShmemInitHash() dropped the max_size parameter (5->4 args)
5. escape_string_warning removed from core_yy_extra_type
6. Missing transitive includes — storage/shmem.h, storage/proc.h, utils/tuplestore.h must
   be explicitly included

Test Failures

• level_tracking regression test needs an alternate expected output for PG19 (immutable SQL
  functions inlined at plan time)
• 018_column_names.pl TAP test needs a PG19 column list entry
• 007_settings_pgsm_query_shared_buffer TAP test needs a .out.19 expected output variant

Fix

PR with full fix: #654

All changes use #if PG_VERSION_NUM >= 190000 / #else / #endif guards. Zero impact on PG
14-18. All 22 regression tests and 34 TAP tests pass.

Suggested solution

No response

Additional context

No response

Code of Conduct

• I agree to follow this project's Code of Conduct

[jeltz]

Thanks, but there is not need for creating issues if you are planning to send a pull request.