visit API should call replaceURL

The `ApplicationInstance`'s `visit()` API currently calls `setURL`, which calls `pushState()` under the hood. Considering the conversation in #18470 where @rwjblue and @chancancode suggested that the `visit` API is intended for booting an application to a custom route (other than `/`), it seems that `visit()` API should use `replaceURL` instead.

https://github.com/emberjs/ember.js/blob/v3.11.1/packages/%40ember/application/instance.js#L268-L275

Here's an example repo: https://github.com/mehulkar/ember-example-visit-api