avformat/avformat: Add FFInputFormat, hide internals of AVInputFormat

This commit does for AVInputFormat what commit
59c9dc82f4 did for AVOutputFormat:
It adds a new type FFInputFormat, moves all the internals
of AVInputFormat to it and adds a now reduced AVInputFormat
as first member.

This does not affect/improve extensibility of both public
or private fields for demuxers (it is still a mess due to lavd).

This is possible since 50f34172e0
(which removed the last usage of an internal field of AVInputFormat
in fftools).

(Hint: tools/probetest.c accesses the internals of FFInputFormat
as well, but given that it is a testing tool this is not considered
a problem.)

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavformat/pdvdec.c

@@ -20,6 +20,7 @@
  */
 
 #include "avformat.h"
+#include "demux.h"
 #include "internal.h"
 
 #define PDV_MAGIC "Playdate VID\x00\x00\x00\x00"
@@ -159,9 +160,10 @@ static int pdv_read_seek(AVFormatContext *s, int stream_index, int64_t timestamp
     return 0;
 }
 
-const AVInputFormat ff_pdv_demuxer = {
-    .name           = "pdv",
-    .long_name      = NULL_IF_CONFIG_SMALL("PlayDate Video"),
+const FFInputFormat ff_pdv_demuxer = {
+    .p.name         = "pdv",
+    .p.long_name    = NULL_IF_CONFIG_SMALL("PlayDate Video"),
+    .p.extensions   = "pdv",
     .priv_data_size = sizeof(PDVDemuxContext),
     .flags_internal = FF_FMT_INIT_CLEANUP,
     .read_probe     = pdv_probe,
@@ -169,5 +171,4 @@ const AVInputFormat ff_pdv_demuxer = {
     .read_packet    = pdv_read_packet,
     .read_close     = pdv_read_close,
     .read_seek      = pdv_read_seek,
-    .extensions     = "pdv",
 };