Fix dead mobs falling asleep (#12917)

* Dead or zombie mobs can no longer sleep

* Removed zombie fix

* Moved dead-checks to OnEvent

* Cleanup

Content.Shared/Bed/Sleep/TryingToSleepEvent.cs

@@ -0,0 +1,8 @@
+namespace Content.Shared.Bed.Sleep;
+
+/// <summary>
+///     Raised by an entity about to fall asleep.
+///     Set Cancelled to true on event handling to interrupt
+/// </summary>
+[ByRefEvent]
+public record struct TryingToSleepEvent(EntityUid uid, bool Cancelled = false);