fix: clip hard edge on web's rtc_video_view

[kNoAPP]

This PR fixes an issue where iOS Safari video box renders would exceed the boundaries set by the RTCVideoViewObjectFit.RTCVideoViewObjectFitContain and RTCVideoViewObjectFit.RTCVideoViewObjectFitCover guidelines.

In the following examples (iOS Safari), I have specified the following:

rtc.RTCVideoView(
  _renderer! as rtc.RTCVideoRenderer,
  mirror: true,
  filterQuality: FilterQuality.medium,
  objectFit: RTCVideoViewObjectFit.RTCVideoViewObjectFitCover,
);

Before this PR

After this PR