Rework permission checks #1168

Job	Run time
Rustfmt	14s
Build docs	1m 20s
Test (MSRV)	1m 17s
Clippy	53s
Test (stable)	1m 59s
Test (beta)	1m 58s
Test (nightly)	1m 46s
Test (macOS)	1m 25s
Test (Windows)	4m 39s
Test (no features)	1m 16s
Test (all features - simdjson, cargo test --all-features --lib --tests --examples)	1m 17s
Test (native TLS, cargo test --all-features --features serenity/native_tls_backend --lib --tests ...	1m 16s
	19m 20s

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