Use re-exports instead of TypeAliases in email.parser (#7665)

stdlib/email/feedparser.pyi

@@ -1,11 +1,12 @@
 from collections.abc import Callable
-from email import _MessageT
 from email.message import Message
 from email.policy import Policy
-from typing import Generic, overload
+from typing import Generic, TypeVar, overload
 
 __all__ = ["FeedParser", "BytesFeedParser"]
 
+_MessageT = TypeVar("_MessageT", bound=Message)
+
 class FeedParser(Generic[_MessageT]):
     @overload
     def __init__(self: FeedParser[Message], _factory: None = ..., *, policy: Policy = ...) -> None: ...