The help panel in GrowthExperiments works on mobile by detaching and appending the overlay. This was done to get around phantom text inputs and scroll issues. This more or less worked until we added search, and now scrolling help panel search results on iOS safari is pretty badly broken, there are also issues with scrolling the home and question review panels.
Rather than fighting against MobileFrontend's overlay system, it would instead be better to integrate the help panel as a proper overlay that MobileFrontend knows about and can load without issue.
- Use two separate call to action modules for desktop and mobile
- Drop ProcessDialog and WindowManager for mobile.
- Refactor help panel code so it's more modular and can be reused outside the process dialog
- Use onBeforeExit (https://gerrit.wikimedia.org/r/c/mediawiki/extensions/MobileFrontend/+/493756/) to avoid warnings about switching to help panel if the user has added text in the editor