pgsql: Fix deferred FK check batching introduced by commit b7b27eb41a5

Fix deferred FK check batching introduced by commit b7b27eb41a5

That commit introduced AfterTriggerIsActive() to detect whether
we are inside the after-trigger firing machinery, so that RI trigger
functions can take the batched fast path. It was implemented using
query_depth >= 0, which correctly identified immediate trigger firing
but missed the deferred case where query_depth is -1 at COMMIT via
AfterTriggerFireDeferred(). This caused deferred FK checks to fall
back to the per-row fast path instead of the batched path.

The correct check is whether we are inside an after-trigger firing
loop specifically. Introduce afterTriggerFiringDepth, a counter
incremented around the trigger-firing loops in AfterTriggerEndQuery,
AfterTriggerFireDeferred, and AfterTriggerSetState, and decremented
after FireAfterTriggerBatchCallbacks() returns. AfterTriggerIsActive()
now returns afterTriggerFiringDepth > 0.

Reported-by: Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com>
Author: Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com>
Co-authored-by: Amit Langote <amitlangote09(at)gmail(dot)com>
Discussion: https://postgr.es/m/C2133B47-79CD-40FF-B088-02D20D654806@gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/5c54c3ed1b934a35a8e9eacff679699ccb3a5070

Modified Files
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src/backend/commands/trigger.c | 26 ++++++++++++++++++++++----
1 file changed, 22 insertions(+), 4 deletions(-)