Rework permission checks #1143

Job	Run time
Clippy	53s
Build docs	1m 20s
Test (MSRV)	1m 19s
Rustfmt	12s
Test (stable)	2m 3s
Test (beta)	2m 0s
Test (nightly)	2m 13s
Test (macOS)	1m 43s
Test (Windows)	4m 12s
Test (no features)	1m 9s
Test (all features - simdjson, cargo test --all-features --lib --tests --examples)	1m 18s
Test (native TLS, cargo test --all-features --features serenity/native_tls_backend --lib --tests ...	1m 13s
	19m 35s

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