[ty] Add support for __all__

crates/ty_python_semantic/resources/mdtest/annotations/stdlib_typing_aliases.md

@@ -102,8 +102,8 @@ reveal_type(SetSubclass.__mro__)
 
 class FrozenSetSubclass(typing.FrozenSet): ...
 
-# TODO: should have `Generic`, should not have `Unknown`
-# revealed: tuple[<class 'FrozenSetSubclass'>, <class 'frozenset'>, Unknown, <class 'object'>]
+# TODO: generic protocols
+# revealed: tuple[<class 'FrozenSetSubclass'>, <class 'frozenset'>, <class 'AbstractSet'>, <class 'Collection'>, <class 'Iterable'>, <class 'Container'>, @Todo(`Protocol[]` subscript), typing.Generic, <class 'object'>]
 reveal_type(FrozenSetSubclass.__mro__)
 
 ####################

crates/ty_python_semantic/resources/mdtest/import/conventions.md

@@ -202,9 +202,9 @@ class AnyFoo: ...
 Here, the symbol is re-exported using the `__all__` variable.
 
 ```py
-# TODO: This should *not* be an error but we don't understand `__all__` yet.
-# error: "Module `a` has no member `Foo`"
 from a import Foo
+
+reveal_type(Foo)  # revealed: <class 'Foo'>
 ```
 
 `a.pyi`:
@@ -221,6 +221,44 @@ __all__ = ['Foo']
 class Foo: ...
 ```
 
+## Re-exports with `__all__`
+
+If a symbol is re-exported via redundant alias but is not included in `__all__`, it shouldn't raise
+an error when using named import.
+
+`named_import.py`:
+
+```py
+from a import Foo
+
+reveal_type(Foo)  # revealed: <class 'Foo'>
+```
+
+`a.pyi`:
+
+```pyi
+from b import Foo as Foo
+
+__all__ = []
+```
+
+`b.pyi`:
+
+```pyi
+class Foo: ...
+```
+
+However, a star import _would_ raise an error.
+
+`star_import.py`:
+
+```py
+from a import *
+
+# error: [unresolved-reference] "Name `Foo` used when not defined"
+reveal_type(Foo)  # revealed: Unknown
+```
+
 ## Re-exports in `__init__.pyi`
 
 Similarly, for an `__init__.pyi` (stub) file, importing a non-exported name should raise an error