[Postgres]: `?` JSON operator cannot be parsed without a space after the field name

When using `PostgreSqlDialect`, the question mark cannot be parsed if it is not followed by a space, whereas postgres accepts the query. The following code panics when parsing `broken`:

```rust
fn main() {
let broken = r#"SELECT user?'adress' FROM my_table"#;
let working = r#"SELECT user? 'adress' FROM my_table"#;

let working_parsed =
sqlparser::parser::Parser::parse_sql(&sqlparser::dialect::PostgreSqlDialect {}, working)
.expect("Failed to parse SQL query");
println!("{:?}", working_parsed);

let broken_parsed =
sqlparser::parser::Parser::parse_sql(&sqlparser::dialect::PostgreSqlDialect {}, broken)
.expect("Failed to parse SQL query");
println!("{:?}", broken_parsed);
}
```

Start by running the supplied Parser::parse_sql example with PostgreSqlDialect and compare the two query forms. Trace how the parser handles ? beside the field name, then add coverage for both spacing forms and confirm the PostgreSQL JSON operator parses without panic.

Written by the indexing model from the issue text.