[PATCH] Introduce unified support for composite GUC options

failed: src/plpgsql_array, src/plpgsql_call, src/plpgsql_control, src/plpgsql_domain, src/plpgsql_misc, src/plpgsql_record, src/plpgsql_simple, src/plpgsql_transaction, src/plpgsql_trap, src/plpgsql_varprops, basic_archive/basic_archive, regress/name, regress/numerology, regress/mvcc, regress/triggers, regress/subselect, regress/case, regress/aggregates, regress/random, regress/arrays, regress/btree_index, regress/brin, regress/gin, regress/join_hash, regress/brin_bloom, regress/brin_multi, regress/merge, regress/misc_functions, regress/collate.icu.utf8, regress/incremental_sort, regress/stats_ext, regress/select_parallel, regress/indirect_toast, regress/json, regress/jsonb, regress/json_encoding, regress/plpgsql, regress/temp, regress/domain, regress/rangefuncs, regress/conversion, regress/alter_table, regress/xml, regress/partition_prune, regress/explain, regress/memoize, regress/stats, regress/oidjoins, regress/fast_default, brin/02_wal_consistency, commit_ts/004_restart, isolation/horizons, isolation/plpgsql-toast