Postgres 16 support for PGSM

* PG16 requires changes around one of the hooks, ifdef added
* Meson build file added

meson.build

@@ -0,0 +1,54 @@
+# Copyright (c) 2022-2023, PostgreSQL Global Development Group
+
+pg_stat_monitor_sources = files(
+  'pg_stat_monitor.c',
+)
+
+pg_stat_monitor = shared_module('pg_stat_monitor',
+  pg_stat_monitor_sources,
+  kwargs: contrib_mod_args + {
+    'dependencies': contrib_mod_args['dependencies'],
+  },
+)
+contrib_targets += pg_stat_monitor
+
+install_data(
+  'pg_stat_monitor.control',
+  'pg_stat_monitor--2.0.sql',
+  'pg_stat_monitor--1.0--2.0.sql',
+  kwargs: contrib_data_args,
+)
+
+tests += {
+  'name': 'pg_stat_monitor',
+  'sd': meson.current_source_dir(),
+  'bd': meson.current_build_dir(),
+  'regress': {
+    'sql': [
+      'application_name',
+      'application_name_unique',
+      'basic',
+      'cmd_type',
+      'counters',
+      'database',
+      'error_insert',
+      'error',
+      'functions',
+      'guc',
+      'histogram',
+      'pgsqm_query_id',
+      'relations',
+      'rows',
+      'state',
+      'tags',
+      'top_query',
+      'user',
+      'version'
+    ],
+    'regress_args': ['--temp-config', files('pg_stat_monitor.conf')],
+    # Disabled because these tests require
+    # "shared_preload_libraries=pg_stat_monitor", which typical
+    # runningcheck users do not have (e.g. buildfarm clients).
+    'runningcheck': false,
+  },
+}