Use private methods instead of symbol keys

[EvanHahn]

This change should have no user impact.

Before:

const kBar = Symbol('bar')

class Foo {
  [kBar]() { /* do something */ }

  twoBars() {
    this[kBar]()
    this[kBar]()
  }
}

After:

class Foo {
  #bar() { /* do something */ }

  twoBars() {
    this.#bar()
    this.#bar()
  }
}

[EvanHahn]

Not sure why, but I was able to remove this @ts-ignore.

[achou11]

lgtm!