Support chained stream

Got compiling error on below code:
```rust
pub fn chained_stream() -> impl Stream {
    #[stream]
    async {
        yield 1;
    }
    .map(|d| d * 2)
}
```

```
error: unexpected token
   --> tests/stream.rs:215:6
    |
215 |     .map(|d| d * 2)
    |      ^^^
```

I think relying on feature `stmt_expr_attributes` would makes a little bit hard to support this.