[ty] Support 'dangling' `type(...)` constructors (#22537)
## Summary
This PR adds support for 'dangling' `type(...)` constructors, e.g.:
```python
class Foo(type("Bar", ...)):
...
```
As opposed to:
```python
Bar = type("Bar", ...)
```
The former doesn't have a `Definition` since it doesn't get bound to a
place, so we instead need to store the `NodeIndex`. Per @MichaReiser's
suggestion, we can use a Salsa tracked struct for this.
