[iOS] Re-add tab event handlers for metadata fetch

[kylehickinson]

This partially reverts a change in #24376 which removed a set of TabEventHandler's

Resolves brave/brave-browser#41208

Submitter Checklist:

• I confirm that no security/privacy review is needed and no other type of reviews are needed, or that I have requested them
• 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 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:

[hffvld]

Verified on iPhone 14 using version(s):

Device/OS: iPhone 14 / iOS 17.7
Brave build: 1.72 (55)
BraveCore: 1.72.55 (129.0.6668.89)

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STEPS:

1. New Install
2. Enable Brave News
3. Navigate to https://en.m.wikipedia.org/wiki/Main_Page or any other article
4. Scroll down the article halfway
5. Open the hamburger menu > Verify that Add Source to Brave News is here
6. Tap Add Source to Brave News > Tap Add
7. Go to Brave News settings > Following > Verify that Wikipedia is added as a source of news

ACTUAL RESULTS:

• Verified that Add Source to Brave News is present in the Hamburger menu
• Verified that the source can be added to the Following sources in Brave News

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