feat: transition to useDefineForClassFields

[EisenbergEffect]

🙋 Feature Request

Transition to useDefineForClassFields for TypeScript.

🤔 Expected Behavior

All core FASTElement and decorator behaviors should continue to work.

😯 Current Behavior

Unknown

💁 Possible Solution

🔦 Context

TypeScript added the option for useDefineForClassFields to enable transpilation of class fields to match the updated ES semantics. We don't know if turning this on will break FAST or not. We need to explore that and see if we will be able to enable this flag for the next version. It is possible that there are decorator incompatibility issues. If that's the case I'd recommend we hold off until the new decorators feature is available in TS and then make the transition to both at the same time.

[EisenbergEffect]

NOTE: If it's possible to turn this on, we still need to benchmark the impact of this change. See this comment tc39/proposal-class-fields#151 (comment) It may be that browsers have not optimized fields yet and switching prior to such optimization would hurt critical scenarios.