NVDEC (H264): Use separate contexts per channel and decode frames in DTS order (#2671)

* Use separate NVDEC contexts per channel (for FFMPEG)

* Remove NVDEC -> VIC frame override hack

* Add missing bottom_field_pic_order_in_frame_present_flag

* Make FFMPEG logging static

* nit: Remove empty lines

* New FFMPEG decoding approach -- call h264_decode_frame directly, trim surface cache to reduce memory usage

* Fix case

* Silence warnings

* PR feedback

* Per-decoder rather than per-codec ownership of surfaces on the cache

Ryujinx.Graphics.Vic/VicRegisters.cs

@@ -4,9 +4,11 @@ namespace Ryujinx.Graphics.Vic
 {
     struct PlaneOffsets
     {
+#pragma warning disable CS0649
         public uint LumaOffset;
         public uint ChromaUOffset;
         public uint ChromaVOffset;
+#pragma warning restore CS0649
     }
 
     struct VicRegisters