Bare literal types (without `Literal`) and support `ForwardRef` in types tracking issue

```py
# from __future__ import annotations
from typing import ForwardRef

def foo(a: "asdf") -> True: # literal string `"asdf"`
...

MyType: TypeAlias = int | ForwardRef("asdf") # a forward reference to the type `asdf`
```

- [x] support non string literal types (#137)
- [x] int
- [x] bool
- [x] Enum
- [ ] tuple
- [ ] support strings as literal types in type annotations (#361)
- [ ] support `ForwardRef` or some alternative in type aliases

An easy route would be to not use `ForwardRef` at all and just force usage of `Literal` in type aliases.

Start with the checklist and review the referenced issues #137 and #361 to understand the existing type-tracking behavior. The remaining scope covers tuple literals, strings as literal types in annotations, and ForwardRef or an alternative in type aliases; done means the selected support is implemented and its behavior is covered by the project’s tests.

Written by the indexing model from the issue text.