perf(reactivity): improve reactive effect memory usage (#4001)

Based on #2345 , but with smaller API change

- Use class implementation for `ReactiveEffect`
- Switch internal creation of effects to use the class constructor
- Avoid options object allocation
- Avoid creating bound effect runner function (used in schedulers) when not necessary.
- Consumes ~17% less memory compared to last commit
- Introduces a very minor breaking change: the `scheduler` option passed to `effect` no longer receives the runner function.

packages/reactivity/src/index.ts

@@ -46,7 +46,9 @@ export {
   resetTracking,
   ITERATE_KEY,
   ReactiveEffect,
+  ReactiveEffectRunner,
   ReactiveEffectOptions,
+  EffectScheduler,
   DebuggerEvent
 } from './effect'
 export { TrackOpTypes, TriggerOpTypes } from './operations'