I'd like to make it the default

Originally posted by @Frenzie in #5899 (comment)

@Frenzie @math-GH I have been increasingly thinking that we should change the views we have by:

1. Merge our normal and reader views
2. Instead, make a new selector (or two - for the vertical and horizontal preferences) to tune the information density:
   • a. when the information density increases horizontally, at some point use the same aside feeds logic than what we have for the mobile view (i.e. collapsed)
     • [Feature] Hide/Unhide sidebar #6119
   • b. the reader view is replaced by the behaviour of the lowest vertical density (articles fully opened by default)
   • d. some of the steps for the vertical density would include allowing two or more lines for the titles, and more or less text preview
     • [Feature] Change thumbnail size #6121
   • e. some of the steps of the horizontal density could control displaying thumbnails or not, just like some of the other columns (in addition to the above-mentioned aside feeds)
3. remove the options for choosing to have the articles opened or closed by default (contributes to simplifying the options), as this becomes redundant with the vertical density selector
4. Keep the preference for the selector level locally on the device, so it is possible to have two different settings for the same account used e.g. on mobile phone, tablet, computer. One setting could be Auto with a heuristic based on window size.
   • [Feature] A way to see more of the title with a mobile device #5899)

An alternative to controlling the horizontal and vertical densities independently would be to offer a few predefined combinations.

In terms of implementation, I do not expect many changes, as it is mostly reworking slightly (and cleaning) what we already have.

Thoughts?