Inconsistent spans for function calls

When using functions spans, it appears that sometimes the closing parenthesis is included, sometimes not.

Consider the following test:

```rust
#[test]
fn test_function_span() {
let sql = "SELECT database(), left(user(),instr(concat(user(),'@'),'@')-1);";
let r = Parser::parse_sql(&crate::dialect::MySqlDialect {}, sql).unwrap();

let query = match &r[0] {
crate::ast::Statement::Query(q) => q,
_ => panic!("Expected query"),
};

let select = match query.body.as_ref() {
crate::ast::SetExpr::Select(s) => s,
_ => panic!("Expected select"),
};

let database_func = match &select.projection[0] {
crate::ast::SelectItem::UnnamedExpr(crate::ast::Expr::Function(func)) => func,
_ => panic!("Expected function expression"),
};
let span = database_func.span();
assert_eq!(span.start, (1, 8).into());
assert_eq!(span.end, (1, 17).into()); // fails here

let left_func = match &select.projection[1] {
crate::ast::SelectItem::UnnamedExpr(crate::ast::Expr::Function(func)) => func,
_ => panic!("Expected function expression"),
};
let span = left_func.span();
assert_eq!(span.start, (1, 20).into());
assert_eq!(span.end, (1, 63).into());
}
```

In both cases, we're testing if the closing parenthesis is included in the span. The first span test for `database_func` fails:

```diff
Diff < left / right > :
-Location(1,16)
+Location(1,17)
```

If I comment that part, the second pair of span assertions passes correctly.

In other words, it seems that we only include closing parentheses for function calls with arguments, but not if there's no argument.

Related: #1548 #1563 #1676

Start with the provided test_function_span case using Parser::parse_sql and MySqlDialect, then trace how function spans are produced for database() and left(...). Compare the span boundaries for calls with and without arguments. Done means both assertions include the closing parenthesis consistently and the test passes.

Written by the indexing model from the issue text.