Fix assumptions in friend DM interactions

[freya022]

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Changes

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Closes Issue: #2817

Description

Since Discord now sends recipients of Friend DMs, assumptions on how to detect friend DMs failed, this is now fixed.

Additionally:

• If the recipient is absent, a warn will be logged and a detached channel will be used
• Bot DMs from interactions will now target the interaction caller, this should be considered as a fix
• Detached private channels will now be able to return an User in some situations
• A new method PrivateChannel#retrieveOpenPrivateChannel() was added, this is intended for cases where the user wants the bot to attempt to send a DM to the friend on which the interaction was called
  • This is necessary as interactions started in friend DMs don't open a channel between the bot and the recipient

[Reddishye]

Awesome! I was just looking for a fork or a pr with this fix (been struggling 30 minutes just to notice it was JDA5 issue)