chore(2916): refactor stream handler for phishing warning and legacy

[DDDDDanica]

Description

As part of https://github.com/MetaMask/MetaMask-planning/issues/2916, it is cleaner to extract the stream out of contentscript file and re-use the logic of phishing stream before implement a new stream.

Related issues

Fixes: https://github.com/MetaMask/MetaMask-planning/issues/2916

Manual testing steps

1. Go to this page...

Screenshots/Recordings

Before

After

Pre-merge author checklist

• I've followed MetaMask Contributor Docs and MetaMask Extension Coding Standards.
• I've completed the PR template to the best of my ability
• I’ve included tests if applicable
• I’ve documented my code using JSDoc format if applicable
• I’ve applied the right labels on the PR (see labeling guidelines). Not required for external contributors.

Pre-merge reviewer checklist

• I've manually tested the PR (e.g. pull and build branch, run the app, test code being changed).
• I confirm that this PR addresses all acceptance criteria described in the ticket it closes and includes the necessary testing evidence such as recordings and or screenshots.

[github-actions]

CLA Signature Action: All authors have signed the CLA. You may need to manually re-run the blocking PR check if it doesn't pass in a few minutes.

[sonarqubecloud]

Quality Gate passed

Issues
7 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[DDDDDanica]

closed due to unknown reason of failed e2e test. start from a clean up-to-date branch and opened PR here
#26526