support AdGuard scriptlet syntax

[antonok-edm]

AdGuard uses #%#//scriptlet(...) for scriptlet injection syntax, whereas uBO filter lists generally use +js(...). AdGuard's syntax requires quoting, which is supported in adblock-rust as of v0.8.3, so it could now be supported as an additional syntax alias.

[superlex]

Good idea. Currently AG filters lists use uBO scriptlet syntax (##+js(...)), but since uBO now supports the AG one (#%#//scriptlet(...)) probably in the future they will use their own syntax.

However, as of now I think is more important adblock-rust supports AdGuard cosmetic filter variants (#236) and other procedural filters (#293) because this will improve adblocking quality a lot.