Simplify media structure inside native ledger

[NejcZdovc]

Resolves brave/brave-browser#4005

Submitter Checklist:

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Verified that these changes build without errors on
  • Windows
  • macOS
  • Linux
• Verified that these changes pass automated tests (npm test brave_unit_tests && npm test brave_browser_tests && npm run test-security) on
  • Windows
  • macOS
  • Linux
• Verified that all lint errors/warnings are resolved (npm run lint)
• Ran git rebase master (if needed).
• Ran git rebase -i to squash commits (if needed).
• Tagged reviewers and labelled the pull request as needed.
• Request a security/privacy review as needed.
• Add appropriate QA labels (QA/Yes or QA/No) to include the closed issue in milestone

Test Plan:

Main thing to test in this PR is if youtube/twitch are working correctly. Twitch has known problems with regards to the panel brave/brave-browser#3590 and brave/brave-browser#3417. In this PR no logic was changed, we just moved code into separate files to simplify code flow.

Things to test:

• media publisher (YT or Twitch) is added to AC table after watching a video
• going to a video you can see media publisher in the panel
• you can tip a media publisher
• for verified media publisher you should see their image in the panel and AC table

Reviewer Checklist:

• New files have MPL-2.0 license header.
• Request a security/privacy review as needed.
• Adequate test coverage exists to prevent regressions
• Verify test plan is specified in PR before merging to source

[ryanml]

Reorganization looks good, test plan worked fine. Twitch panel issue was noted (Consistently saw twitch.com in the panel, but publishers filled the AC table with the expected name)