Emit a new UpdateEvent

[alies-dev]

UpdateEvent event back-ported from SDK v4.

Differences with SDKv4 events:

• event from SDKv4 has public Bot $bot, in current PR it's public Api $telegram;. Reason -- there is no Bot class in SDK v3.
• in this PR this event extends \League\Event\AbstractEvent (because we use league/event events system here), in SDK v4 it doesn't extend any classes.
• this PR has better test than in SDK v4 :)

Challenges

SDK v3 has a weird feature, I don't know a reason why we have it. This is $shouldEmitEvent parameter:

// in Update.php trait
public function getWebhookUpdate($shouldEmitEvent = true, ...

I decided to not touch it, always emit a new event and keep emitting the old one UpdateWasReceived depends on $shouldEmitEvent argument's value. Reason - it provides more consistency with SDK v4.

[irazasyed]

Thank you 👍