Improve tokens semantics and clean up gateway feature gates #5794

Job	Run time
Test (nightly)	1m 14s
Test (macOS)	1m 18s
Build docs	21s
Check minimal versions	29s
Test (stable)	2m 37s
Examples	39s
Test (beta)	2m 14s
Test (Windows)	4m 0s
Test (native-tls)	2m 13s
MSRV	0s
Test (no default features)	34s
Test (no cache)	2m 10s
Test (no gateway)	1m 37s
Test (unstable Discord API features)	2m 30s
Test (chrono, chrono)	39s
Test (unstable API + typesize, default unstable typesize, true)	40s
Test (builder without model, builder, true)	17s
Test (unstable Discord API (no default features), unstable, true)	15s
	23m 47s

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