[Brave News] Fix direct feeds and favicon sizes

[fallaciousreasoning]

Resolves brave/brave-browser#26368
Resolves brave/brave-browser#26339

Submitter Checklist:

• I confirm that no security/privacy review is needed, or that I have requested one
• There is a ticket for my issue
• Used Github auto-closing keywords in the PR description above
• Wrote a good PR/commit description
• Squashed any review feedback or "fixup" commits before merge, so that history is a record of what happened in the repo, not your PR
• Added appropriate labels (QA/Yes or QA/No; release-notes/include or release-notes/exclude; OS/...) to the associated issue
• Checked the PR locally: npm run test -- brave_browser_tests, npm run test -- brave_unit_tests, npm run lint, npm run gn_check, npm run tslint
• Ran git rebase master (if needed)

Reviewer Checklist:

• A security review is not needed, or a link to one is included in the PR description
• New files have MPL-2.0 license header
• Adequate test coverage exists to prevent regressions
• Major classes, functions and non-trivial code blocks are well-commented
• Changes in component dependencies are properly reflected in gn
• Code follows the style guide
• Test plan is specified in PR before merging

After-merge Checklist:

• The associated issue milestone is set to the smallest version that the
  changes has landed on
• All relevant documentation has been updated, for instance:
  • https://github.com/brave/brave-browser/wiki/Deviations-from-Chromium-(features-we-disable-or-remove)
  • https://github.com/brave/brave-browser/wiki/Proxy-redirected-URLs
  • https://github.com/brave/brave-browser/wiki/Fingerprinting-Protections
  • https://github.com/brave/brave-browser/wiki/Brave%E2%80%99s-Use-of-Referral-Codes
  • https://github.com/brave/brave-browser/wiki/Custom-Headers
  • https://github.com/brave/brave-browser/wiki/Web-Compatibility-Exceptions-in-Brave
  • https://github.com/brave/brave-browser/wiki/QA-Guide
  • https://github.com/brave/brave-browser/wiki/P3A

Test Plan:

[brave-builds]

A Storybook has been deployed to preview UI for the latest push

[simonhong]

++ it would be great to have a test case for ShouldDisplayFeedItem() changes.

[brave-builds]

A Storybook has been deployed to preview UI for the latest push

[stephendonner]

Verified PASSED using

Brave	1.47.36 Chromium: 107.0.5304.91 (Official Build) nightly (x86_64)
Revision	3d5948960d62418160796d5831a4d2d7d6c90fa8-refs/branch-heads/5304@{#1097}
OS	macOS Version 11.7.1 (Build 20G918)

brave/brave-browser#26368:

1. install 1.47.36
2. launch Brave
3. set brave://flags/#brave-news-v2 to Enabled
4. set brave://flags/#brave-news-subscribe-button to Enabled
5. click Relaunch
6. open a new-tab page
7. scroll down
8. click on Show Brave News
9. click on Customize
10. type common under Discover
11. click on Follow
12. compare the favicon to the larger one in Sources

Confirmed favicons are now right-sized

brave/brave-browser#26339:

1. install 1.47.36
2. launch Brave
3. open a new-tab page
4. click on Customize
5. click on Brave News
6. type https://www.rt.com/rss-feed/ into Feed URL
7. click Add source
8. close the dialog
9. scroll down
10. click on Show Brave News
11. scroll more
12. confirmed I saw an `RT.com - Daily news article
13. opened brave://flags
14. set brave://flags/#brave-news-v2 to Enabled
15. clicked on Relaunch
16. scrolled a lot
17. looked for RT.com - Daily news

Confirmed both the RT.com source as well as the previously-viewed (in News v1) article is still present

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