PG19: build foundation (source-level compat, scaffold ruleutils_19.c, CI image bump)

[ihalatci]

DESCRIPTION: Add PG19 build support; extension compiles and loads.

First PR of the PG19 enablement series tracked in #8597. Achieves
source-level compatibility with PG19 (pg19devel) and a clean
CREATE EXTENSION citus while keeping PG17 and PG18 builds green.
Regression-test correctness and PG19 feature integration are tackled
in follow-up PRs against the pg19-support development branch.

What changed

Source-level PG19 compat

• configure.ac / configure / pg_version_constants.h: accept PG19,
  add PG_VERSION_19 (and a PG_VERSION_20 placeholder).
• src/include/pg_version_compat.h: centralised PG19 source-compat
  shims (PageSetChecksumInplace, replorigin_session_origin,
  GetPublicationRelations, pg_plan_query / standard_planner /
  planner signatures, FuncnameGetCandidates, ShmemInitHash 4-arg
  form, ExecInitScanTupleSlot / table_beginscan flags, LWLock
  tranche, NamedLWLockTranche, ClusterStmt → RepackStmt
  indirection, standard_conforming_strings helper, bits16 /
  fmStringInfo, RepOriginId / InvalidRepOriginId, query_instr).
• Distributed/columnar source updates for renamed / retyped APIs:
  PGPROC->links->waitLink, ClusterStmt indirection,
  Instrumentation / NodeInstrumentation split,
  pgstat_report_vacuum PG19 signature, get_relation_info_hook
  gating, columnar PageSetChecksum shim.
• Header hygiene: add pg_version_compat.h / fmgr.h / storage/fd.h
  / tuplestore.h / lwlock / shmem includes wherever transitive
  includes no longer pull them in under PG19.
• resource_lock.h: bump PG_MAJORVERSION_NUM static-assert ceiling
  to ≤ 19.

Compiler-warning (-Werror) fixes

• Source-level fixes across ~76 files to build clean under PG19's
  stricter warnings (old-style foo() → (void) prototypes,
  strict-prototype forward declarations, -Wimplicit-fallthrough
  annotations, new switch arms, etc.). No compiler-flag
  demotion — the build stays on the same warning/error flags as
  PG17/PG18; warnings are resolved at the source rather than silenced.

Shmem sizing

• shared_library_init.c: add 128 KB of shmem slack on PG19 to absorb
  the new cache-line alignment overhead now that ShmemInitHash
  allocates all hash elements up-front. Heuristic — sized
  empirically against current Citus shmem consumers; revisit if a
  consumer is added.
• maintenanced.c: drop a pre-existing double-count of hash size in
  ShmemInitStruct sizing. Only exposed because PG19's new
  ShmemInitHash pre-allocates the buckets. Bundled here because the
  fix is required for the PG19 build to load; called out separately
  so reviewers don't read it as scope creep.

Deparser (scaffold only)

• ruleutils_19.c: scaffold only in this PR. Per the precedent
  set by PG17 compatibility: ruleutils #7725 (PG17) and Pg18 ruleutils adaptation #8010 (PG18), the deparser file lands in
  its own PR (PR1b). PR1 ships the file as a clone of ruleutils_18.c
  retargeted at the PG19 version guard so the binary links. Running
  the regression suite against PR1 alone produces 18 failures in
  check-multi and many more in check-multi-mx — silent
  PG18-on-PG19 deparse corruption. PR1b imports a proper upstream PG19
  ruleutils via 3-way merge and brings the suite to 191/191 + 68/69.
• .gitattributes: exclude ruleutils_19.c from citus-style
  (-citus-style). The file is an upstream-derived clone (~12k lines)
  and exceeds the CI uncrustify (citus_indent 0.68.1) 10,000-line
  limit, which otherwise aborts the style check.

CI

• Bump image_suffix in .github/workflows/build_and_test.yml from
  -dev-fa732cb to -dev-e11d99c so CI pulls the test-image set
  that includes PG19 bits. The same change bumps the PG minors to
  16.14 / 17.10 / 18.4.
• Add pg19_version to the params block and wire it into the build
  matrix. PG19 (19devel) is also wired into the pg-upgrade jobs:
  the test-pg-upgrade matrix gains 18 → 19 and 16 → 19 pairs and
  upgrade_pg_versions becomes 16.14-17.10-18.4-19devel.
• PG19 is intentionally not added to test-citus,
  test-citus-failure, test-citus-cdc, or the test-citus-upgrade
  job. The regression suite requires the upstream-derived
  ruleutils_19.c that lands in PR1b, and no released Citus supports
  PG19 yet (so Citus-version upgrade testing on PG19 is not meaningful).
  Until PR1b lands, only the build and pg-upgrade paths are meaningful
  on PG19.

Validation

• PG19devel: build exits 0, CREATE EXTENSION citus succeeds.
• PG17.10: build exits 0 (regression guard).
• PG18.4: build exits 0 (regression guard).
• No regression-suite changes here; correctness work is split into
  subsequent PRs against pg19-support.

Non-goals / follow-ups

• The real deparser port is PR1b — do not run the regression suite
  or any production workload on PG19 before PR1b lands.
• multi_explain.c is touched here for the Instrumentation /
  NodeInstrumentation rename only. A separate TupleDescFinalize
  runtime fix lands in PR2.

Refs: #8597

[codecov]

Codecov Report

❌ Patch coverage is 62.58503% with 55 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.69%. Comparing base (10c3a8b) to head (9637d6b).

Additional details and impacted files

@@               Coverage Diff                @@
##           pg19-support    #8600      +/-   ##
================================================
- Coverage         88.75%   88.69%   -0.07%     
================================================
  Files               288      288              
  Lines             64289    64350      +61     
  Branches           8090     8091       +1     
================================================
+ Hits              57062    57075      +13     
- Misses             4889     4936      +47     
- Partials           2338     2339       +1     

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[ihalatci]

Superseded by #8601, which restructures the same change set into 5 reviewable commits (ruleutils_19.c isolated into a single commit, -Werror fixes separated from the deparser scaffold, CI collapsed to one commit) and rebases onto the refreshed pg19-support branch. Closed in favour of #8601.