MoonBit parser compatibility frontend for moon-audit

Based on moonbitlang/parser 0.4.0 (Apache-2.0).
Legacy Loop and TryOperatorKind::Question nodes and Handrolled productions
are restored from moonbitlang/parser 0.3.0, with original source positions.
MoonYacc remains the unmodified current-syntax fallback; no legacy yacc
grammar/table regeneration is claimed. Package imports/format configuration
are adjusted for the vendored package location.

See vendor.lock.json for exact sources and hashes, and compat.patch for all
changes from 0.4.0. Lexical errors are additionally retained by both parser
entry paths so recovered ASTs cannot be reported as successful input. This is a modified frontend, not an official parser release.
Legacy syntax support is not legacy security-semantics support.
