fix: treat a positional parameter '?' as a valid end of the ternary then-branch

[fudianchn]

What

A ternary whose then-branch ends with a plain positional parameter parses as a TernaryExpression again:

SELECT a ? ? : c FROM t
SELECT a ? b + ? : c FROM t
SELECT a ? ? : ? FROM t

Why / Root cause

Follow-up to #2476, found while regression-testing the snapshot build (reported in #2476 (comment)): canEndExpression() whitelisted S_PARAMETER ($N style) but not the bare ?. The bare ? is an anonymous token (no token-kind constant, outside the non-reserved range), so the scan skipped the : closing the then-branch and the parser silently committed to the jsonb reading. On current master the statements above parse as JsonOperator(a, JsonExpression(?:c)) while 7b64825 still parsed them as TernaryExpression(a, JdbcParameter, c) (regression). In the wrong tree the ? is no longer a JdbcParameter node (relevant for parameter extraction), and the wrong AST deparse round-trips stably (a ? ?:c), which is why the existing round-trip case did not catch it.

How

Add || "?".equals(t.image) to the default branch of canEndExpression(), the same image comparison already used for ")" and "]": a positional parameter is a complete primary expression, so a : directly after it closes the then-branch. The ?| / ?& operators have different images and are unaffected. The statements fixed by #2476 are unaffected as well: there the : follows null or an operator token, so the new check is not reached (j ? :key, j ? 'k' AND x = :p, j ? ? all keep their current reading).

Scope

One condition in the ternary-vs-jsonb disambiguation predicate plus an AST-shape regression test; grammar productions and AST classes are untouched.

Testing

TernaryExpressionTest.testTernaryWithPositionalParameterThenBranch pins the AST shape (root TernaryExpression, then-branch JdbcParameter / Addition, else-branch Column): it fails on current master with ClassCastException: JsonOperator cannot be cast to TernaryExpression and passes with this change. The round-trip list gains SELECT a ? b + ? : c FROM t and SELECT a ? ? : ? FROM t. All 45 TernaryExpressionTest tests pass with this change.

Performance

gradle jmh, JSQLParserBenchmark.parseSQLStatements on performance.sql, version=latest, 10 forks x 10 iterations (100 samples per run, two interleaved runs per build) on a 32-core host:

build	ms/op
master (5080d19)	3.731 ± 0.023 / 3.748 ± 0.029
this PR (21ac7c4)	3.760 ± 0.029 / 3.736 ± 0.021

The two builds interleave across the repeated runs (pair 1: +0.78%, pair 2: -0.32%); every delta lies within the 99.9% confidence intervals: no regression.