Add rv annotaton to send_static_file() (#4216)

Author: AMDmi3

third_party/2and3/flask/helpers.pyi

@@ -19,7 +19,7 @@ def flash(message: Any, category: str = ...) -> None: ...
 def get_flashed_messages(with_categories: bool = ..., category_filter: Any = ...): ...
 def send_file(filename_or_fp: Any, mimetype: Optional[Any] = ..., as_attachment: bool = ..., attachment_filename: Optional[Any] = ..., add_etags: bool = ..., cache_timeout: Optional[Any] = ..., conditional: bool = ..., last_modified: Optional[Any] = ...) -> Response: ...
 def safe_join(directory: Any, *pathnames: Any): ...
-def send_from_directory(directory: Any, filename: Any, **options: Any): ...
+def send_from_directory(directory: Any, filename: Any, **options: Any) -> Response: ...
 def get_root_path(import_name: Any): ...
 def find_package(import_name: Any): ...
 
@@ -44,7 +44,7 @@ class _PackageBoundObject:
     def has_static_folder(self): ...
     def jinja_loader(self): ...
     def get_send_file_max_age(self, filename: Any): ...
-    def send_static_file(self, filename: Any): ...
+    def send_static_file(self, filename: Any) -> Response: ...
     def open_resource(self, resource: Any, mode: str = ...): ...
 
 def total_seconds(td: Any): ...