Better signatures for methods that accept structured content

[shayypy]

Primer

Currently, most methods fitting this description have a signature like this:

async def method(*content, **kwargs):
    ...

... Which is not great for usability. The optimal signature is seen in methods like Messageable.send and ChatMessage.edit:

async def method(
    *pos_content: Optional[Union[str, Embed, File, Emoji, Member]],
    content: Optional[str] = MISSING,
    file: Optional[File] = MISSING,
    files: Optional[Sequence[File]] = MISSING,
    embed: Optional[Embed] = MISSING,
    embeds: Optional[Sequence[Embed]] = MISSING,
    ...
):
    ...

This provides a better typing experience & allows the user to pass content positionally (better for user accounts) or via a keyword-argument (discord.py-compatible & good for consistency).

To-do

• [ ] ChatMessage.create_thread
• [ ] Messageable.create_thread
• [x] User.send
• [ ] Reply.reply
• [ ] Reply.edit
• [ ] Doc.edit
• [ ] Doc.reply
• [ ] DocsChannel.create_doc
• [ ] ForumTopic.reply
• [ ] ForumTopic.edit
• [x] ForumChannel.create_topic
• [ ] Announcement.reply
• [ ] Announcement.edit
• [ ] AnnouncementChannel.create_announcement
• [ ] Media.reply
• [x] ListItem.edit
  • This was a breaking change that changed how editing list item notes worked with this method. ListItemNote.edit should be used instead, but a new note_content can also be passed to ListItem.edit.
• [x] ListItem.create_item
• [x] ListItemNote.edit
• [x] ListChannel.create_item