Fixes to lists-showcase styling/code

[cdrini]

Closes #7704 (Addendum)

Finished some of the design details in figma + DRYed up some of the code.

Technical

Code:

• Used BEM notation correctly; the code was already structured BEM-like, but was using - instead of __ to denote child relationship
• The HTML had a few unnecessary nesting/divs; dropped those
• I18n all the strings
• Fix some bugs in the code (eg default parameters cannot be lists)
• Used larger covers since they're displayed larger than the -S
• Used less position: absolute in the list-card
• Used CSS to truncate title, not manual limiting to 16 characters

UI:

• I removed the gradient at the end ; that's a pretty common UI affordance for scrolling; we should bring back now that scrolling is enabled, but it takes a bit of time since you have to make it appear/disappear as necessary.
• Added a "see all" button at end now that it's scrollable
• The covers ended up a touch easier staggered; I like the effect so kept it in

Testing

Tested ~latest Chrome, FF, and Safari (iPad).

Screenshot

Stakeholders

@mekarpeles

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 16.12%. Comparing base (c8203dd) to head (f0b3908).
Report is 95 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9412      +/-   ##
==========================================
- Coverage   16.13%   16.12%   -0.02%     
==========================================
  Files          92       90       -2     
  Lines        4766     4758       -8     
  Branches      827      828       +1     
==========================================
- Hits          769      767       -2     
+ Misses       3480     3471       -9     
- Partials      517      520       +3     

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[cdrini]

Auto-merging this one as an addendum to #8878 , since some feedback got lost during the CR process. Usually wouldn't auto-merge such a large one, but need the style fixes to go out before the deploy. I QA'd on testing on a few different devices/via browserstack. Assigning to you @mekarpeles for a post-merge review 👍