Make VideoFrameType an enum class, and move to separate file and target

Bug: webrtc:5876, webrtc:6883
Change-Id: I1435cfa9e8e54c4ba2978261048ff3fbb993ce0e
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/126225
Commit-Queue: Niels Moller <nisse@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27239}
diff --git a/modules/video_coding/packet_buffer.cc b/modules/video_coding/packet_buffer.cc
index 11cc06e..804ce4a 100644
--- a/modules/video_coding/packet_buffer.cc
+++ b/modules/video_coding/packet_buffer.cc
@@ -126,7 +126,7 @@
 
     int64_t now_ms = clock_->TimeInMilliseconds();
     last_received_packet_ms_ = now_ms;
-    if (packet->frameType == kVideoFrameKey)
+    if (packet->frameType == VideoFrameType::kVideoFrameKey)
       last_received_keyframe_packet_ms_ = now_ms;
 
     found_frames = FindFrames(seq_num);
@@ -378,9 +378,11 @@
         const size_t first_packet_index = start_seq_num % size_;
         RTC_CHECK_LT(first_packet_index, size_);
         if (is_h264_keyframe) {
-          data_buffer_[first_packet_index].frameType = kVideoFrameKey;
+          data_buffer_[first_packet_index].frameType =
+              VideoFrameType::kVideoFrameKey;
         } else {
-          data_buffer_[first_packet_index].frameType = kVideoFrameDelta;
+          data_buffer_[first_packet_index].frameType =
+              VideoFrameType::kVideoFrameDelta;
         }
 
         // If this is not a keyframe, make sure there are no gaps in the