Scoped EVM queue ID class

[Bushstar]

Summary

• Creates a class that will create and destroy an EVM queue ID
• Only create a queue if EVM is enabled, allows the replacement, where applicable, of the isEvmEnabledForBlock check with a valid EVM queue ID check

Implications

• Storage

  • Database reindex required
  • Database reindex optional
  • Database reindex not required
  • None

• Consensus

  • Network upgrade required
  • Includes backward compatible changes
  • Includes consensus workarounds
  • Includes consensus refactors
  • None

[prasannavl]

@Bushstar nice work. I think we can do better though.

I think this might have complicated things a bit with isValid, as well as checking the count manually; and what happens when the count isn't.

However, this might be perfect for shared_ptr itself, who's whole goal is to keep track of these and destroy when everything goes out of scope automatically. By wrapping it and adding a destructor on top, I think we've actually increased complexity than simplify it.

Rather, how about, create a simple scope wrapper, who's destructor will always destroy the queue. Now, we keep track of that in the shared_ptr and pass the shared_ptr around. So, it has to be:

shared_ptr<ScopedCQueue> -- this automatically reference tracks the queue, and destroys it when all references go out of scope.