T360753: Update preview layout

[medied]

https://phabricator.wikimedia.org/T360753

Update to accommodate for new design layout: wikimedia/wikipedia-preview#218. This comes from a sync with Sudhanshu, we are bringing back the gallery and we're leaving the scroll cue

[stephanebisson]

I see a few strange things with this PR.

1. I can't scroll the preview content
2. I don't see the scroll cue
3. The "read on wikipedia" link after the content is not styled correctly (see screenshot below)

[medied]

@stephanebisson I'm not able to replicate those from my end, but I have seen such strange things before like the "read on wikipedia" missing styling and the scrolling issue. Can you confirm you still see those after npm link again with the main branch from core and trying it out on different posts and previews? Usually takes a dance of rebuilding on both the core and the plugin, might need to run the postinstall script manually on plugin side

[stephanebisson]

I redid the npm link dance and it works now.