Cosmetic filter - use !important for display property

[rulatir]

Test plan

See brave/brave-core#3121

Description

The cosmetic filters don't work with elements that set the display property using the style attribute.

Proposed solution: in the rule created by the cosmetic filter, the display property should be !important.

Please implement!

[Detailed STR on PR]

[srirambv]

Probably covered under #904

[rulatir]

Please give it a minute of your time to actually look into the issue. The element in question has an id attribute, so the style rule injected by the cosmetic filter is super simple:

#element-id {
   display: none;
}

But the element has style attribute with display: block, so this overrides display: none in the injected stylesheet. It's pure CSS as CSS behaves. Nothing to analyse further. This has nothing to do with wrong element being matched. Replacing the unique-selector library will not fix this. No tweaks to the selector of the cosmetic filter's rule will fix this. The element being matched is the right one, it's just that the cosmetic filter's style rule is too weak.