sql: reject out-of-range routine placeholders

[Alignyx]

Fixes #172995.

Root cause

Routine placeholder lookup returned nil for two different states: no active routine-argument scope, and an active scope in which the requested ordinal was out of range. The placeholder visitor could not distinguish those states, so an invalid routine placeholder fell through to ordinary prepared-statement placeholder construction. When the surrounding statement had a value for that ordinal, the routine body could read and fold the caller's placeholder value instead of raising an undefined-parameter error.

How I tracked it down

The two higher-level lazy routine paths from the report are not currently executable on master: nested routine DDL is rejected by the routine DDL safety check, and dynamic EXECUTE is not implemented. I therefore isolated the shared optbuilder transition under an active outer placeholder assignment. The control cases showed that an ordinary prepared placeholder correctly became a constant and a valid routine ordinal correctly became a routine parameter column, while an out-of-range routine ordinal incorrectly became the caller's constant. That placed the first invalid transition at the boundary between routine scope lookup and generic placeholder handling rather than in lazy body construction itself.

Fix

The existing single-value scope lookup remains available to its other callers, and a companion lookup now reports whether an ordinal is definitively out of range. Placeholder resolution uses that result to preserve valid routine parameter columns and to raise the existing no value provided for placeholder error before generic placeholder construction when an active routine scope rejects the ordinal.

Test coverage

• Added TestRoutineParamOrdinalIsolation with three arms: ordinary prepared placeholders still use their assigned values, valid routine ordinals still resolve to parameter columns, and invalid routine ordinals return SQLSTATE 42P02 even when the caller has a value at that position.
• Ran the full optbuilder test target and the existing regression_143887 and regression_144020 routine-placeholder logic regressions.
• Ran the complete PL/pgSQL UDF logic suite in local, fake-distributed, and local-prepared configurations, plus the complete SQL UDF logic suite locally.

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