Show which tabs are unloaded

[is-this-c]

Introduces Edge's simple and intuitive behavior in which unloaded tabs are distinguished from loaded tabs. This behavior replaces Chromium's behavior in which unloaded tabs are not distinguished from loaded tabs except where a tab is proactively discarded.

Resolves https://github.com/brave/brave-browser/issues/36720.

I checked this PR locally. It is working. Your developer config however appears to be broken and so a few tests for unrelated things fail.

Submitter Checklist:

• [x] I confirm that no security/privacy review is needed and no other type of reviews are needed, or that I have requested them
• [x] There is a ticket for my issue
• [x] Used Github auto-closing keywords in the PR description above
• [x] 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
• [x] Checked the PR locally:
  • npm run test -- brave_browser_tests, npm run test -- brave_unit_tests wiki
  • npm run presubmit wiki, 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/Web-Compatibility-Exceptions-in-Brave
  • [ ] https://github.com/brave/brave-browser/wiki/QA-Guide
  • [ ] https://github.com/brave/brave-browser/wiki/P3A

Test Plan:

1. Restore a session so that we'll have unloaded tabs that weren't discarded.
2. Visit brave://discards.
3. Click Urgent Discard for a tab.
4. Click Proactive Discard for another tab.
5. Right click Tab Discard (Suspender) and select Discard active tab only.
6. Click Tab Discard (Suspender) in another tab to externally discard it and quickly switch away to avoid reloading.
7. Unloaded tabs should be visually distinguishable instead of just proactively discarded tabs.