Rewrite permission checks #1187

Job	Run time
Build docs	1m 29s
Clippy	48s
Test (MSRV)	1m 21s
Rustfmt	8s
Test (stable)	2m 11s
Test (beta)	2m 10s
Test (nightly)	1m 48s
Test (macOS)	2m 14s
Test (Windows)	4m 54s
Test (no features)	1m 12s
Test (all features - simdjson, cargo test --all-features --lib --tests --examples)	1m 12s
Test (native TLS, cargo test --all-features --features serenity/native_tls_backend --lib --tests ...	1m 17s
	20m 44s

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