Rework Appearance Page to match iOS

The changes can be found in this iOS pull request. https://github.com/shiftyjelly/pocketcasts-ios/pull/3672

> It's been a long standing pet peeve (and a source of some user complaints) that when you choose to follow the iOS light/dark mode in our app things get a bit confusing. Mainly that:
>
> - there's no indication of how to select the dark theme the app will use
> - if you tap on a light theme while in dark mode, or a dark theme while in light mode the setting gets toggled off
> - our hidden long press to toggle theme gesture gets triggered accidentally or if people are doing it on purpose it has the same issue as above.

https://user-images.githubusercontent.com/308331/178376626-42b9991a-9606-4f6b-89e3-c04c9b781b40.mp4

No Android files, tests, or entry points are named. Start by reviewing the linked iOS pull request and the screenshots, then locate the Android Appearance page; done means its theme-selection behavior and presentation match the referenced iOS design.

Written by the indexing model from the issue text.