A flag to treat third-party `Any` as `object`/`Untyped`

The flag will default to false and will be mandatory for all targets.

Eg:
thirdparty.pyi
```py
def foo(a: list[Any]) -> Any: ...
```

my.py
```py
from thirdparty import foo
reveal_type(foo) # def (a: list[object]) -> object

a: int = foo([1]) # error: expression has type "object" variable has type "int"
```

I don't see any value in converting it to `Untyped` or showing an error that a parameter is typed as `Any`, how would you be able to do anything to fix it?

Start by tracing how the checker processes third-party stubs such as thirdparty.pyi and propagates Any into my.py, including reveal_type output. Define the flag's behavior and target requirements from the examples, then verify the resulting type of foo and the assignment error.

Written by the indexing model from the issue text.