Fix jsify on function

[renefloor]

Fixes #60

As explained in the thread in #60, there are 2 issues.

First it says there is no forEach on Instance of 'RtcStatsReport', which is weird, as that should exists, but stats is of type dynamic. This is fixed by setting the type of stats to RTCStatsReport.

When you do that you get parameter 1 is not of type 'Function'.. That's because jsify only works on primitives, so it converts the function to a generic object. By using toJS is converts the function to a JSExportedDartFunction.

Also fixes: flutter-webrtc/flutter-webrtc#1781 and flutter-webrtc/flutter-webrtc#1788

[EvertonMJunior]

Awesome @renefloor! Given that discovery, wouldn't it be valid to apply the same patch on lib\src\rtc_rtp_receiver_impl.dart (line 33) and lib\src\rtc_rtp_sender_impl.dart (line 101)? They use the same conversion of a Dart function with jsify.

[renefloor]

Good catch! Fixed it in 5c489db

Quickly went through the other uses of jsify, but looks like they were all on maps, lists and strings.

[EvertonMJunior]

Perfect, just tested it on release mode too and this seems to solve the issue completely, no more errors.

[cloudwebrtc]

lg!