Create Shields UX to indicate when blocking might be breaking a site

[tildelowengrimm]

From #1025.

I think there are two parts to this:
Design the UX: Should this be like the autoplay blocked UI? Should it match Chromium's site-settings blocking icon format?
Tune the Behavior: Should this happen every time device recognition or cookies or something else is blocked? That presents an over-notification and annoyance risk. Should we use some heuristic to estimate when it might be causing problems? What heuristic?

[NumDeP]

1 - When you're on a site which is breaking because of Shields, you sometimes feel like you're looking at where's wally until you realise there's a problem and you don't know what aspect is actually blocking the site from functioning effectively and unfortunately have to turn off Shields and let everything in just to get it running as intended, when it might just be one blocked thing causing the issue.
For a browser that's suppose to save time and presents that visually, this process usually wastes a lot of time. That's not a dig at the team but just my opinion that it would be wicked if you could moved it up a notch to P3 :)

2 - Wouldn't it help the team if we were to use this issue to list all the sites that are not currently/properly functional with Shields on, this way you could improve Shield's blocking feature and improve the UX of this feature?

3 - As for the behaviour, I don't know what exactly it was but something from the team during the development of the Muon version gave me the impression that something clever would happen behind the scenes of Brave's engine, that would essentially allow users to easily access a website without any hassle which is prohibiting a user to effectively peruse it and not to forget, sites that also have anti-ad blocking mechanisms that don't allow users to access articles. Was I wrong to think this?

4 - I think it would be good to have this discussion in connection with #4246 & #1926 as it relates to onboarding and how it could be bothersome for new users and possibly integrate the UX, understandably with different text.

Thanks