fix: update messageCount/totalMessageSent on message events

[almeidx]

Please describe the changes this PR makes and why it should be merged:

The message_count and total_message_sent fields on threads created in a forum will increment on MESSAGE_CREATE and will decrement on MESSAGE_DELETE/MESSAGE_DELETE_BULK. There will be no CHANNEL_UPDATE event through gateway notifying those fields' changes (similar to last_message_id changes). Clients should update those values when receiving corresponding events.

https://discord.com/developers/docs/topics/threads#forums

Status and versioning classification:

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Name	Status	Preview	Updated
discord-js	✅ Ready (Inspect)	Visit Preview	Sep 19, 2022 at 0:37AM (UTC)

[codecov]

Codecov Report

Merging #8635 (8162d5b) into main (8444576) will decrease coverage by 13.31%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##              main    #8635       +/-   ##
============================================
- Coverage   100.00%   86.68%   -13.32%     
============================================
  Files           39       87       +48     
  Lines         3199     8784     +5585     
  Branches       410     1110      +700     
============================================
+ Hits          3199     7614     +4415     
- Misses           0     1128     +1128     
- Partials         0       42       +42     

Flag	Coverage Δ
builders	100.00% <ø> (ø)
collection	100.00% <ø> (?)
proxy	74.10% <ø> (?)
rest	91.99% <ø> (?)
utilities	100.00% <ø> (?)
voice	63.86% <ø> (?)
ws	60.47% <ø> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
packages/voice/src/audio/AudioPlayerError.ts	0.00% <0.00%> (ø)
packages/voice/src/receive/AudioReceiveStream.ts	100.00% <0.00%> (ø)
packages/ws/src/strategies/sharding/worker.ts	0.00% <0.00%> (ø)
...ackages/rest/src/lib/handlers/SequentialHandler.ts	86.03% <0.00%> (ø)
packages/voice/src/audio/PlayerSubscription.ts	50.00% <0.00%> (ø)
packages/voice/src/receive/SSRCMap.ts	86.20% <0.00%> (ø)
packages/voice/src/audio/AudioPlayer.ts	80.95% <0.00%> (ø)
packages/ws/src/utils/utils.ts	100.00% <0.00%> (ø)
...es/ws/src/strategies/sharding/IShardingStrategy.ts	100.00% <0.00%> (ø)
packages/rest/src/lib/errors/HTTPError.ts	100.00% <0.00%> (ø)
... and 38 more

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