Add `ShardAction::Dispatch` variant #1071

Job	Run time
Test (nightly)	59s
Test (macOS)	1m 2s
Check minimal versions	26s
Test (stable)	47s
Test (beta)	1m 2s
Build docs	40s
Examples	2m 1s
Test (Windows)	2m 4s
Test (native-tls)	1m 49s
Test (no default features)	43s
Test (no cache)	2m 1s
Test (no gateway)	1m 26s
Test (unstable Discord API features)	46s
Test (zlib compression)	2m 16s
Test (zstd compression)	2m 18s
Test (zlib and zstd compression)	1m 55s
Test (chrono, chrono)	40s
Test (unstable API + typesize, default unstable typesize, true)	55s
Test (builder without model, builder, true)	32s
Test (unstable Discord API (no default features), unstable, true)	17s
MSRV	0s
	24m 39s

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