Adding generator_stop to compile_future_features (#5320)

* Adding generator_stop to compile_future_features.

* Removing expected failure from PEP 479 unit test.

Lib/test/test_contextlib.py

@@ -197,8 +197,6 @@ class ContextManagerTestCase(unittest.TestCase):
                 else:
                     self.fail(f'{stop_exc} was suppressed')
 
-    # TODO: RUSTPYTHON
-    @unittest.expectedFailure
     def test_contextmanager_except_pep479(self):
         code = """\
 from __future__ import generator_stop

compiler/codegen/src/compile.rs

@@ -2904,8 +2904,7 @@ impl Compiler {
             match feature.name.as_str() {
                 // Python 3 features; we've already implemented them by default
                 "nested_scopes" | "generators" | "division" | "absolute_import"
-                | "with_statement" | "print_function" | "unicode_literals" => {}
-                // "generator_stop" => {}
+                | "with_statement" | "print_function" | "unicode_literals" | "generator_stop" => {}
                 "annotations" => self.future_annotations = true,
                 other => {
                     return Err(self.error(CodegenErrorType::InvalidFutureFeature(other.to_owned())))