Add support for function result attributes.

This allows dialect-specific attributes to be attached to func results. (or more specifically, FunctionLike ops).

For example:

```
func @f() -> (i32 {my_dialect.some_attr = 3})
```

This attaches my_dialect.some_attr with value 3 to the first result of func @f.

Another more complex example:

```
func @g() -> (i32, f32 {my_dialect.some_attr = "foo", other_dialect.some_other_attr = [1,2,3]}, i1)
```

Here, the second result has two attributes attached.

PiperOrigin-RevId: 275564165