Refactor FXIOS-10096 [WIP] Content blocking: cleanup, refactors + support for custom JSON lists

[mattreaganmozilla]

📜 Tickets

Jira ticket

💡 Description

Clean-up and refactors to our content blocking code. Primarily this is for improvements to readability and performance but it also adds support for custom-loading content lists; right now this feature is entirely for developer convenience and has no effect for end users, but it will allow us to test custom content blocker lists more easily in the app moving forward.

Please note: all of this code is (to some extent) an ongoing WIP as we are currently exploring improvements to our ad-blocking. Additional changes will likely be forthcoming.

📝 Checklist

You have to check all boxes before merging

• Filled in the above information (tickets numbers and description of your work)
• Updated the PR name to follow our PR naming guidelines
• Wrote unit tests and/or ensured the tests suite is passing
• When working on UI, I checked and implemented accessibility (minimum Dynamic Text and VoiceOver)
• If needed, I updated documentation / comments for complex code and public methods
• If needed, added a backport comment (example @Mergifyio backport release/v120)

[thatswinnie]

Would it be possible to add unit tests for the ad blocker?

[mattreaganmozilla]

Would it be possible to add unit tests for the ad blocker?

@thatswinnie Yes that's definitely on the radar, though I think it will likely be revisited after we have a more concrete plan for the ad-blocking updates.