Prepare for splitting FrameType into AudioFrameType and VideoFrameType

This cl deprecates the FrameType enum, and adds aliases AudioFrameType
and VideoFrameType.

After downstream usage is updated, the enums will be separated
and be moved out of common_types.h.

Bug: webrtc:6883
Change-Id: I2aaf660169da45f22574b4cbb16aea8522cc07a6
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/123184
Commit-Queue: Niels Moller <nisse@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27011}

modules/video_coding/encoded_frame.h

@@ -67,7 +67,7 @@ class VCMEncodedFrame : protected EncodedImage {
   /**
    *   Get frame type
    */
-  webrtc::FrameType FrameType() const { return _frameType; }
+  webrtc::VideoFrameType FrameType() const { return _frameType; }
   /**
    *   Get frame rotation
    */