[VL] Skip escape arg when offloading Like with no-backslash pattern

[zhulipeng]

What changes are proposed in this pull request?

When offloading Like to Velox, omit the escape literal argument and emit
the 2-arg form (like(input, pattern)) when both:

1. the pattern is a constant Literal, and
2. the escape char is Spark's default \ AND the pattern does not contain \.

Otherwise we still emit the 3-arg form (like(input, pattern, escape)) as before.

Why are the changes needed?

Spark's Like node always carries an escapeChar (defaulting to \) even when
the SQL did not specify ESCAPE. We previously always sent the 3-arg form to
Velox, which forces Velox's makeLike (Re2Functions.cpp) to take the
escape-aware path: parsePattern runs an extra unescape pass, and
determinePatternKind runs with escapeChar.has_value() == true, even when
no actual escaping is needed.

When the pattern literal contains no \, the 2-arg and 3-arg forms are
semantically identical, so we can safely send the cheaper 2-arg form. Velox
already registers both signatures via likeSignatures().

How was this patch tested?

• Existing Like query coverage in VeloxStringFunctionsSuite (like /
  rlike / ilike) — query results unchanged.
• TPC-H Q13 end-to-end run at 6 TB scale — see Performance section.
• ./dev/format-scala-code.sh clean.

Performance

TPC-H Q13 @ 6 TB scale: >6% end-to-end latency reduction.

Q13's l_comment NOT LIKE '%special%requests%' filter scans every lineitem row.
With the 3-arg form, the constant-pattern fast paths in determinePatternKind
are bypassed and Velox falls back to the generic LikeWithRe2 path, which
hot-loops in re2::DFA::InlinedSearchLoop — CPU profiling shows
InlinedSearchLoop accounts for >8% of total cycles on Q13.

Sending the 2-arg form lets determinePatternKind recognize this as the
kSubstrings shape and dispatch to the dedicated OptimizedLike<kSubstrings>
kernel, eliminating the RE2 DFA cost. No regression observed on other queries.

Was this patch authored or co-authored using generative AI tooling?

Reviewed-by: Claude claude-opus-4-7