Send thread member objects when connecting to the gateway

[APixelVisuals]

The guild create events that are sent when connecting to the gateway don't provide all the thread member objects in the guild aside from the client user. This data should be sent if the bot has the guild members intent enabled and can be useful for bots that need to state manage thread members.

[ajpalkovic]

I would recommend including a few specific and real use cases
As is, we don't really see this as something that's common or all that important, so isn't likely to get prioritized!