perf(reactivity): improve reactive effect memory usage

[yyx990803]

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. Only component update effects will need to create a bound copy of the runner.

Consumes ~17% less memory compared to last commit (which already improved the memory usage a bit) when creating computed/watch/watchEffect (image showing benchmark of creating 10k each).

Introduces a very minor breaking change: the scheduler option passed to effect no longer receives the runner function. Instead, simply call the reference of the returned runner:

const run = effect(() => {}, {
  scheduler: () => {
    run()
  }
})