[reopen] [cr84] Settings page follow-ups: fixes guest mode, and refactors to overrides by module name

[petemill]

Reopening as #5976 was reverted in cr84. Android build was failing due to trying to minify the JS which was included as binary data (or maybe it was compressed). But now we have merged to master a change that prevents android compiling settings webui, which was never intended for android.

• Fix settings page in guest mode windows, use and override page visibility correctly
• Brings back the row divider lines for brave items.
• Refactor all settings webui overrides to be in modules with the name of the overriden component, as per the new README.md:

Use this directory to add modifications to any chromium polymer module.
Steps to take:
- Create a JS module which calls any of the polymer_overriding exported functions, e.g. `RegisterStyleOverride`.
- Import the module to the index.js inside this directory.
- Include the module in settings_resources.grd.

Fix brave/brave-browser#5065
Fix brave/brave-browser#2995

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
  • Android
  • iOS
  • Linux
  • macOS
  • Windows
• Verified that these changes pass automated tests (unit, browser, security tests) on
  • iOS
  • Linux
  • macOS
  • Windows
• 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
• Public documentation has been updated as necessary. 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-issues-with-tracking-protection
  • https://github.com/brave/brave-browser/wiki/QA-Guide

Test Plan:

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

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.

[petemill]

Everything CI passed, except audit_deps which is marked as unstable

[bsclifton]

++

[mkarolin]

++

[bsclifton]

Uplifted to 1.11 with #5996