to-do: remove use of `protected`, `private` and `public` from `@std/data-structures`

[iuioiua]

We should use #private or regular properties instead of these access modifiers. This work was essentially done in https://github.com/denoland/deno_std/pull/4793/commits/5b86a65872ecdfcb7454646416577cab4c7811b7 but was then later reverted.