Function try_dispatch 

pub fn try_dispatch(
    name: &str,
    args: &[RValue],
    _named: &[(String, RValue)],
    env: &Environment,
) -> Option<Result<RValue, RError>>

Try to dispatch an rlang FFI function by symbol name.

Returns Some(result) if the symbol was handled, None to fall through to the native C code path.