support for `scoped` and `local` default instances

The attribute `default_instance` currently does not support `local` and `scoped` modifiers. 
Motivation:
```
/-- info: 1 + 2 : Nat -/
#guard_msgs in #check 1 + 2

@[local default_instance 101]  -- Error: `default_instance` must be global
instance instOfNatInt (n : Nat) : OfNat Int n where
  ofNat := n

/-- info: 1 + 2 : Int -/
#guard_msgs in #check 1 + 2

```