Parse negative numbers for Postgres Dialect

[kwannoel]

Parser should parse negative numbers as is, rather than into a unary_op neg, wrapping an inner value, to be consistent with Postgres.

Postgres behaviour using (pglast):

[nix-shell:~/projects/risingwave-nix]$ ./query_parser.py "select -(-(-(9223372036854775808)))"
{'@': 'SelectStmt',
 'all': False,
 'limitOption': {'#': 'LimitOption',
                 'name': 'LIMIT_OPTION_DEFAULT',
                 'value': 0},
 'op': {'#': 'SetOperation', 'name': 'SETOP_NONE', 'value': 0},
 'targetList': ({'@': 'ResTarget',
                 'location': 7,
                 'val': {'@': 'A_Const',
                         'location': 7,
                         'val': {'@': 'Float',
                                 'val': Decimal('-9223372036854775808')}}},)}

[kwannoel]

To reproduce:

use sqlparser::dialect::PostgreSqlDialect;
use sqlparser::parser::Parser;

fn main() {
    let sql = "SELECT -9223372036854775808;";
    let dialect = PostgreSqlDialect {};

    let ast = Parser::parse_sql(&dialect, sql).unwrap();

    println!("AST: {:#?}", ast);
}

Output:

AST: [
    Query(
        Query {
            with: None,
            body: Select(
                Select {
                    distinct: false,
                    top: None,
                    projection: [
                        UnnamedExpr(
                            UnaryOp {
                                op: Minus,
                                expr: Value(
                                    Number(
                                        "9223372036854775808",
                                        false,
                                    ),
                                ),
                            },
                        ),
                    ],
                    into: None,
                    from: [],
                    lateral_views: [],
                    selection: None,
                    group_by: [],
                    cluster_by: [],
                    distribute_by: [],
                    sort_by: [],
                    having: None,
                    qualify: None,
                },
            ),
            order_by: [],
            limit: None,
            offset: None,
            fetch: None,
            lock: None,
        },
    ),
]