Mark rules with `webrtc` option as invalid in the browser extension

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:
```adblock
@@||moeni.net^$document,stealth=webrtc
```
the filter will be converted to:
```adblock
@@||moeni.net^$document
```
Therefore, it causes https://github.com/AdguardTeam/AdguardFilters/issues/169648#issuecomment-1879274118.

Screenshots