Mark rules with webrtc option as invalid in the browser extension

[piquark6046]

Currently, AdGuard Browser Extension does not understand $stealth modifier with webrtc option.
If any filter with the $stealth=webrtc applied, the request or document will be allowed as a normal exception.

For example, if there is a filter as the following:

@@||moeni.net^$document,stealth=webrtc

the filter will be converted to:

@@||moeni.net^$document

Therefore, it causes AdguardTeam/AdguardFilters#169648 (comment).

Screenshots

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It is impossible to disable webrtc by website. So we can just to not add such rules in the extension.