Revert of Delete unused and almost unused frame-related methods. (patchset #12 id:220001 of https://codereview.webrtc.org/2065733003/ )

Reason for revert:
Breaks downstream applications which inherits webrtc::VideoFrameBuffer and tries to override deleted methods data(), stride() and MutableData().

Original issue's description:
> Delete unused and almost unused frame-related methods.
>
> webrtc::VideoFrame::set_video_frame_buffer
> webrtc::VideoFrame::ConvertNativeToI420Frame
>
> cricket::WebRtcVideoFrame::InitToBlack
>
> VideoFrameBuffer::data
> VideoFrameBuffer::stride
> VideoFrameBuffer::MutableData
>
> TBR=tkchin@webrtc.org # Refactoring affecting RTCVideoFrame
> BUG=webrtc:5682
>
> Committed: https://crrev.com/76270de4bc2dac188f10f805e6e2fb86693ef864
> Cr-Commit-Position: refs/heads/master@{#13183}

TBR=perkj@webrtc.org,pbos@webrtc.org,marpan@webrtc.org,tkchin@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=webrtc:5682

Review-Url: https://codereview.webrtc.org/2076113002
Cr-Commit-Position: refs/heads/master@{#13184}

webrtc/sdk/objc/Framework/Classes/RTCVideoFrame.mm

@@ -40,42 +40,42 @@
   if (!self.i420Buffer) {
     return nullptr;
   }
-  return self.i420Buffer->DataY();
+  return self.i420Buffer->data(webrtc::kYPlane);
 }
 
 - (const uint8_t *)uPlane {
   if (!self.i420Buffer) {
     return nullptr;
   }
-  return self.i420Buffer->DataU();
+  return self.i420Buffer->data(webrtc::kUPlane);
 }
 
 - (const uint8_t *)vPlane {
   if (!self.i420Buffer) {
     return nullptr;
   }
-  return self.i420Buffer->DataV();
+  return self.i420Buffer->data(webrtc::kVPlane);
 }
 
 - (int32_t)yPitch {
   if (!self.i420Buffer) {
     return 0;
   }
-  return self.i420Buffer->StrideY();
+  return self.i420Buffer->stride(webrtc::kYPlane);
 }
 
 - (int32_t)uPitch {
   if (!self.i420Buffer) {
     return 0;
   }
-  return self.i420Buffer->StrideU();
+  return self.i420Buffer->stride(webrtc::kUPlane);
 }
 
 - (int32_t)vPitch {
   if (!self.i420Buffer) {
     return 0;
   }
-  return self.i420Buffer->StrideV();
+  return self.i420Buffer->stride(webrtc::kVPlane);
 }
 
 - (int64_t)timeStamp {