email: add Message methods (#6731)

Add `email.message.Message` methods, mark `email.iterators.walk` as wontfix

stdlib/email/message.pyi

@@ -69,6 +69,9 @@ class Message:
         replace: bool = ...,
     ) -> None: ...
     def __init__(self, policy: Policy = ...) -> None: ...
+    # The following two methods are undocumented, but a source code comment states that they are public API
+    def set_raw(self, name: str, value: str) -> None: ...
+    def raw_items(self) -> Iterator[tuple[str, str]]: ...
 
 class MIMEPart(Message):
     def __init__(self, policy: Policy | None = ...) -> None: ...

tests/stubtest_allowlists/py3_common.txt

@@ -391,6 +391,7 @@ email.contentmanager.get_text_content
 email.contentmanager.set_bytes_content
 email.contentmanager.set_message_content
 email.contentmanager.set_text_content
+email.iterators.walk
 
 # Side effects from module initialization
 _compat_pickle.excname
@@ -628,10 +629,7 @@ email.feedparser
 email.generator
 email.header
 email.iterators
-email.iterators.walk
 email.message
-email.message.Message.raw_items
-email.message.Message.set_raw
 email.mime
 email.parser
 email.quoprimime