[ty] Add support for dynamic `type()` classes (#22291)
## Summary
This PR adds support for dynamic classes created via `type()`. The core
of the change is that `ClassLiteral` is now an enum:
```rust
pub enum ClassLiteral<'db> {
/// A class defined via a `class` statement.
Stmt(StmtClassLiteral<'db>),
/// A class created via the functional form `type(name, bases, dict)`.
Functional(FunctionalClassLiteral<'db>),
}
```
And, in turn, various methods on `ClassLiteral` like `body_scope` now
return `Option` or similar (and callers must adjust to that change in
signature).
Over time, we can expand the enum to include functional namedtuples,
etc. (I already have this working in a separate branch, and I believe it
slots in well.)
(I'd love help with the names -- I think `StmtClassLiteral` is kind of
lame. Maybe `DeclarativeClassLiteral`?)
Closes https://github.com/astral-sh/ty/issues/740.
---------
Co-authored-by: Alex Waygood <alex.waygood@gmail.com>
