DuckDB V2 PEG-based SQL parser

DuckDB v2.0 replaces its PostgreSQL-derived SQL parser with a new PEG-based parser that is easier to maintain and evolve while allowing runtime extensions. The new parser maintains the same functionality for users while improving DuckDB's ability to support its growing SQL dialect, which includes unique features like GROUP BY ALL and SELECT * EXCLUDE. This upgrade happens transparently to users and represents a significant internal improvement to how DuckDB validates SQL syntax before execution.