avcodec.h: split AVPacket API into its own header

doc/APIchanges

@@ -15,6 +15,9 @@ libavutil:     2017-10-21
 
 API changes, most recent first:
 
+2020-xx-xx - xxxxxxxxxx - lavc 58.78.100 - avcodec.h packet.h
+  Move AVPacket-related public API to new header packet.h.
+
 2020-03-29 - xxxxxxxxxx - lavf 58.42.100 - avformat.h
   av_read_frame() now guarantees to handle uninitialized input packets
   and to return refcounted packets on success.

libavcodec/Makefile

@@ -12,6 +12,7 @@ HEADERS = ac3_parser.h                                                  \
           dxva2.h                                                       \
           jni.h                                                         \
           mediacodec.h                                                  \
+          packet.h                                                      \
           qsv.h                                                         \
           vaapi.h                                                       \
           vdpau.h                                                       \

libavcodec/avpacket.c

@@ -26,9 +26,10 @@
 #include "libavutil/internal.h"
 #include "libavutil/mathematics.h"
 #include "libavutil/mem.h"
-#include "avcodec.h"
+
 #include "bytestream.h"
 #include "internal.h"
+#include "packet.h"
 
 void av_init_packet(AVPacket *pkt)
 {