vvcdec doesn't set pict_type and AV_FRAME_FLAG_KEY in the output

[rgonzalezfluendo]

Update VVC decoder to set frames info, useful with ffprobe and other tools.

How to reproduce:

$ wget  https://www.itu.int/wftp3/av-arch/jvet-site/bitstream_exchange/VVC/draft_conformance/draft6/CodingToolsSets_E_Tencent_1.zip
$ unzip CodingToolsSets_E_Tencent_1.zip CodingToolsSets_E_Tencent_1.bit
$ ffprobe -hide_banner CodingToolsSets_E_Tencent_1.bit -select_streams v -show_frames -show_entries frame=pict_type,key_frame -of csv

Output:

frame,0,?
frame,0,?
frame,0,?
frame,0,?
frame,0,?
frame,0,?
frame,0,?
frame,0,?
frame,0,?

Expected output

frame,1,I
frame,0,B
frame,0,B
frame,0,B
frame,0,B
frame,0,B
frame,0,B
frame,0,P
frame,0,B

from https://ffmpeg.org//pipermail/ffmpeg-devel/2025-January/338109.html