Add getting cache flags from events

[freya022]

Pull Request Etiquette

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Changes

• [X] Internal code
• [X] Library interface (affecting end-user code)
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Closes Issue: NaN

Description

Allows getting cache flags from events, also fixes documented requirements of scheduled events, and clarifies permission overrides events

Replaces getting cache flags / gateway intents using annotations

[freya022]

For reference, here is how https://github.com/discord-jda/JDA/pull/2558/commits/aa6788daae50067eed066933f56b0d49e2f60f87 is made: Generate requirement annotations.patch