Add flags support for ':matches-css()' regex patterns

[ameshkov]

@realodix commented on Thu Nov 25 2021

Looks like AdGuard doesn't support regex flags for :matches-css(). I didn't notice until I saw AdguardTeam/AdguardFilters#101083 and read the documentation, because in the diff.txt file there is no message.

<style type="text/css">
  #to-be-blocked::before {
    content: "Advertisement"
  }
</style>
<div id="to-be-blocked" class="banner"></div>
<div id="not-to-be-blocked" class="banner"></div>

##div.banner:matches-css-before(content: /adv/i)

uBO requires using the i flag to be case insensitive.

https://github.com/gorhill/uBlock/wiki/Procedural-cosmetic-filters#subjectmatches-cssarg