Add support for new `POLL_RESULT` and `PURCHASE_NOTIFICATION` message types #5519

Job	Run time
Test (stable)	3m 7s
Test (beta)	3m 15s
Test (Windows)	5m 10s
Test (macOS)	1m 52s
Test (native-tls)	2m 53s
Test (no default features)	48s
MSRV	47s
Test (no cache)	2m 59s
Test (nightly)	3m 8s
Test (no gateway)	1m 48s
Test (unstable Discord API features)	3m 12s
Test (simd-json)	3m 12s
Build docs	37s
Test (chrono, chrono)	45s
Test (unstable API + typesize, default unstable_discord_api typesize, true)	1m 15s
Examples	3m 48s
Test (builder without model, builder, true)	38s
Check minimal versions	36s
Test (unstable Discord API (no default features), unstable_discord_api, true)	26s
	40m 16s

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