UX: Fix several issues with topic progress refactor (PR #14790)

This helps avoid jumpiness on mobile when transitioning quckly from the topic list and into a topic. Delaying the transition means there is less movement on the page on first load when routing straight to the end of a topic.

(The issue was most noticeable in the DiscourseHub app.)

GitHub

The title of this pull request changed from “UX: Add tiny delay to topic progress transitions” to "UX: Add delay to topic progress transitions, fix Android infinite scroll issue

The title of this pull request changed from “UX: Add delay to topic progress transitions, fix Android infinite scroll issue” to "UX: Fix several issues with topic progress refactor