[Feature Request][compiler] warning on field selection

[rahxephon89]

🚀 Feature Request

Motivation

Given the following enum type:

enum E<T1, T2> has key {
  V1{name: T1}
  V2{name: T2}
}

Whether field selection v.0 for value v of type E pass compilation depends on type instantiation of T1 and T2. We may want to generate a warning for this.