WT-1543: Blog index styles

[lucianoratamero]

One-line summary

This PR implements all styles needed for the blog index page, and double checks other pages, like the /all/ and /topics/ pages.

Significant changes and points to review

• Removed dates and tags from article list items on the index, all and article pages (not present in Figma). This also removed the localized-tag-name test, since tags are no longer rendered in those lists.
• Blog CSS consolidated/simplified and colors + spacing normalized; shared fl-blog-body class added to all blog page templates.
• The topics list carousel was kept as is, since it looks very misaligned on figma, and it works both functionally and visually as-is.

Issue / Bugzilla link

https://mozilla-hub.atlassian.net/browse/WT-1543

Testing

Run the fixtures, then manually check the blog index, /all, topic filter and article pages in light and dark themes.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.08%. Comparing base (938bebe) to head (a2c49e9).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1757   +/-   ##
=======================================
  Coverage   90.08%   90.08%           
=======================================
  Files         182      182           
  Lines       13219    13229   +10     
=======================================
+ Hits        11908    11918   +10     
  Misses       1311     1311           

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[maribedran]

Images are right-aligned on the topic page and are too small. This looks like a side effect of some other change here.

[lucianoratamero]

Images are right-aligned on the topic page and are too small. This looks like a side effect of some other change here.

this was on purpose. we don't have Figma designs for the topic pages (or I couldn't find any), so I just mirrored what we have for the designs of the "All topics" page.
it does clash with the left-aligned ones in the main page (the "latest posts" section, but there are a lot of these small inconsistencies that I tried to iron out. I'm totally open to discuss and modify them, though!

[maribedran]

@lucianoratamero there aren't specific designs for it, but I'm assuming it should look the same as the index page, since it's the same layout.

[maribedran]

The topics list isn't scrolling all the way to the beginning.