support types that are defined with values

```py
a: Final = 1
A = Literal[a]
# okay, because `a` is always 1

b: a = a
# okay, because `a` is always 1

class C ...
c: Final = C()
d: c = c # error
# bad because it's ambigious if the `c` here means instance `C` or `type[C]`, need to use `TypeOf[c]`
```

# use case

```py
@global_enum
class _A(Enum):
A = 1
A: Final = _A.A

a: _A.A = A # works
a: A = A # desired
```

The issue provides Python examples using Final, Literal, Enum, and the proposed TypeOf syntax, but names no source files or tests. Start by reproducing the examples with the current type checker and tracing how these annotations are interpreted. Done means the stated value-defined type cases are supported without making the ambiguous class-instance case silently valid.

Written by the indexing model from the issue text.