Rework permission checks #1173

Job	Run time
Rustfmt	9s
Clippy	51s
Build docs	1m 21s
Test (MSRV)	1m 14s
Test (stable)	1m 2s
Test (beta)	1m 15s
Test (nightly)	1m 12s
Test (macOS)	1m 54s
Test (Windows)	2m 23s
Test (no features)	1m 12s
Test (all features - simdjson, cargo test --all-features --lib --tests --examples)	1m 6s
Test (native TLS, cargo test --all-features --features serenity/native_tls_backend --lib --tests ...	1m 4s
	14m 43s

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