sql: reject qualified column names that match whole-row references

[Alignyx]

SELECT t1.t1 FROM t1 returned a whole-row record when t1 contained only f1. A predicate such as WHERE t1.t1 IS NULL could therefore silently test the row instead of reporting a missing column.

Restrict optbuilder's whole-row fallback to unqualified references. Qualified missing columns now preserve the original undefined-column error (42703); bare whole-row references and real columns retain their behavior. Add seven native optbuilder regression cases covering qualified names, aliases, predicates, multiple sources, CTEs, derived tables, and correlation.

Fixes #120625.

Related PR: #173881 also addresses this issue. This PR contains an independently generated fix with regression coverage in optbuilder's data-driven tests.

Validation:

• Confirmed that the new regression file fails before the fix and passes afterward.
• Built and ran the complete //pkg/sql/opt/optbuilder:optbuilder_test executable on this branch: 109 tests and subtests passed, with no skips.
• Executed 20 SQL cases twice against real single-node test servers and an additional exact-row assertion: 41/41 checks passed. All valid-query rows matched the original baseline, including bare rows, aliases, existing same-named columns, stars, tuple fields, and correlated queries.
• crlfmt -fast -tab 2 and git diff --check passed.

The product fix and regression fixture were generated using DeepSeek, then reviewed and validated locally. Local native test binaries were built with Bazel using --norun_validations; the ./dev wrapper refuses to run in this root execution environment. Full-repository generation and lint are not claimed here.

Release note (bug fix): Fixed a bug where a qualified reference to a nonexistent column, such as SELECT t1.t1 FROM t1, could silently return an entire table row. Such references now report an undefined-column error (SQLSTATE 42703). Unqualified whole-row references such as SELECT t1 FROM t1 and references to existing columns remain valid.

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