Add supportsNativeHandle to the RTCVideoEncoder protocol.

The simulcast_encoder_adapter expects codecs that specify
supports_native_handle to perform resampling/scaling (through
GetEncoderInfo).
This change adds a method to the RTCVideoEncoder to let objc encoders
specify this rather than relying on the default.

Bug: webrtc:13044
Change-Id: I2efcbd42aa4f2048285f451c7b691fdeca111e62
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/227641
Reviewed-by: Kári Helgason <kthelgason@webrtc.org>
Commit-Queue: Peter Hanspers <peterhanspers@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#34683}

sdk/objc/api/video_codec/RTCWrappedNativeVideoEncoder.mm

@@ -79,4 +79,8 @@
   return NO;
 }
 
+- (BOOL)supportsNativeHandle {
+  RTC_NOTREACHED();
+  return NO;
+}
 @end