[C++] Substrait: add mappings for starts_with, ends_with and match_substring #50988

starts_with, ends_with and match_substring have no Substrait mapping, so expressions using them cannot be serialized.

import pyarrow as pa
import pyarrow.compute as pc
from pyarrow.substrait import serialize_expressions

schema = pa.schema([pa.field("cat", pa.string())])
serialize_expressions([pc.starts_with(pc.field("cat"), "al")], ["f"], schema)

pyarrow.lib.ArrowNotImplementedError: No conversion function exists to convert
the Arrow function starts_with to a Substrait call

Same for pc.ends_with and pc.match_substring. Comparisons, isin and arithmetic all serialize fine, so this looks like a per-function gap rather than a structural one.

Substrait defines starts_with, ends_with and contains in functions_string.yaml, which cover all three.

The signatures differ: the Substrait functions take the pattern as a second argument, while the Arrow kernels are unary and carry it in MatchSubstringOptions. So the mapping needs the second argument to be a string literal. Substrait's case_sensitivity option maps onto ignore_case, except for CASE_INSENSITIVE_ASCII which has no Arrow equivalent.

This matters for engines that ingest a PyArrow filter through Substrait, where an unmappable function turns into a hard failure rather than a fallback.

Component(s)

C++, Python