obs-ffmpeg: Include avcodec header for AVCodecContext

FFmpeg commit e67e02d15672 [1] drops avcodec.h from avformat.h includes.
Therefore we need to include it explicitly.

[1]: https://github.com/FFmpeg/FFmpeg/commit/e67e02d15672a87da1b0566e197a1e19dc7e1e33
     lavf/avformat.h: drop the avcodec.h include

plugins/obs-ffmpeg/ffmpeg-mux/ffmpeg-mux.c

@@ -27,6 +27,7 @@
 #include "ffmpeg-mux.h"
 
 #include <util/dstr.h>
+#include <libavcodec/avcodec.h>
 #include <libavformat/avformat.h>
 
 #define ANSI_COLOR_RED "\x1b[0;91m"

plugins/obs-ffmpeg/obs-ffmpeg-formats.h

@@ -1,5 +1,7 @@
 #pragma once
 
+#include <libavcodec/avcodec.h>
+
 static inline int64_t rescale_ts(int64_t val, AVCodecContext *context,
 				 AVRational new_base)
 {

plugins/obs-ffmpeg/obs-ffmpeg-nvenc.c

@@ -24,6 +24,7 @@
 
 #include <libavutil/opt.h>
 #include <libavutil/pixdesc.h>
+#include <libavcodec/avcodec.h>
 #include <libavformat/avformat.h>
 
 #include "obs-ffmpeg-formats.h"

plugins/obs-ffmpeg/obs-ffmpeg-output.h

@@ -2,6 +2,7 @@
 
 #include <libavutil/opt.h>
 #include <libavutil/pixdesc.h>
+#include <libavcodec/avcodec.h>
 #include <libavformat/avformat.h>
 #include <libswscale/swscale.h>