Rework permission checks #1174

Job	Run time
Clippy	59s
Rustfmt	9s
Build docs	1m 26s
Test (MSRV)	1m 31s
Test (stable)	2m 5s
Test (beta)	2m 7s
Test (nightly)	1m 46s
Test (macOS)	1m 46s
Test (Windows)	4m 43s
Test (no features)	1m 19s
Test (all features - simdjson, cargo test --all-features --lib --tests --examples)	1m 13s
Test (native TLS, cargo test --all-features --features serenity/native_tls_backend --lib --tests ...	1m 19s
	20m 23s

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