Add a 1st party check to the SelectorsPollerScript.js (non-aggressive cosmetic filtering)

[cuba]

Description:

We use aggressive cosmetic filtering in iOS. In order to make it non-aggressive we need to add a 1st party check on element urls. Currently the check in hard coded to return false except for some small edge cases like relative URLs. The difficulty in doing this is we have to do it asynchronously as we need to talk back to iOS to do a proper etld+1 check.

The idea is to

1. Add a mutation observer that looks for images and videos
2. Every time it gets one, extract the domain for it, and pass it async to iOS to get a yes/no isFirstParty value
3. Keep track of all the answers you’ve gotten for the current page in a Brave maintained Map
4. Check that map in the cosmetic filtering isFirstParty function
5. Re-check ads where isFirstParty() returns false every time you get a new answer from 2

Once this is done we need to remove the temporary exception we have added to https://github.com/brave/adblock-lists/blob/master/brave-lists/brave-ios-specific.txt

[cuba]

Done with the following PR: #7333