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

[KotlinIsland]

# 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.

[KotlinIsland]

What about dict and Protocol literals?

a: {'a': int, 'b': str} = {'a': 1, str}
def (a: Protocol[{'a': int, 'b': str}]): ...