Implement VP9 loop filtering (#550)

Unmerged PR from OG Ryujinx (#4367). From @gdkchan:

> The main goal of this change is porting the loop filtering from
libvpx, which should fix the block artifacts on some VP9 videos on games
using NVDEC to decode them. In addition to that, there are two other
changes:
> 
> - The remaining decoder code required to decode a VP9 video (with
headers included) has been added. That was done because it's much better
to test the decoder standalone with a video file. I decided to keep that
code on the emulator, even if some of it is unused, since it makes
standalone testing easier in the future too, and we can include unit
tests with video files.
> - Large refactoring of both new and existing code to conform with our
conding [sic] styles, done by @TSRBerry (thanks!) Some of it has been
automated.
> 
> Since we had no loop filtering before, this change will make video
decoding slower. That may cause frame drop etc if the decoder is not
fast enough in some games. I plan to optimize the decoder more in the
future to make up for that, but if possible I'd prefer to not do it as
part of this PR, but if the perf loss is too severe I might consider.
> 
> This will need to be tested on games that had the block artifacts, it
would be nice to confirm if they match hardware now, and get some
before/after screenshots etc.

Comment from @Bjorn29512:

> Significantly improves the block artifacts in FE: Engage.
> 
> Before:
>
![](https://user-images.githubusercontent.com/110204265/216882414-ec88dbda-7544-4490-8a47-37f074056ae3.png)
> 
> After:
>
![](https://user-images.githubusercontent.com/110204265/216882478-4e81fead-1033-4877-b282-f9cac6d6aa3b.png)

---------

Co-authored-by: gdkchan <gab.dark.100@gmail.com>
Co-authored-by: TSR Berry <20988865+TSRBerry@users.noreply.github.com>

src/Ryujinx.Graphics.Nvdec.Vp9/FrameBuffers.cs

@@ -0,0 +1,79 @@
+using Ryujinx.Common.Memory;
+using Ryujinx.Graphics.Nvdec.Vp9.Common;
+using Ryujinx.Graphics.Nvdec.Vp9.Types;
+
+namespace Ryujinx.Graphics.Nvdec.Vp9
+{
+    internal struct InternalFrameBuffer
+    {
+        public ArrayPtr<byte> Data;
+        public bool InUse;
+    }
+
+    internal struct InternalFrameBufferList
+    {
+        public ArrayPtr<InternalFrameBuffer> IntFb;
+    }
+
+    internal static class FrameBuffers
+    {
+        public static int GetFrameBuffer(MemoryAllocator allocator, Ptr<InternalFrameBufferList> cbPriv, ulong minSize,
+            ref VpxCodecFrameBuffer fb)
+        {
+            int i;
+            Ptr<InternalFrameBufferList> intFbList = cbPriv;
+            if (intFbList.IsNull)
+            {
+                return -1;
+            }
+
+            // Find a free frame buffer.
+            for (i = 0; i < intFbList.Value.IntFb.Length; ++i)
+            {
+                if (!intFbList.Value.IntFb[i].InUse)
+                {
+                    break;
+                }
+            }
+
+            if (i == intFbList.Value.IntFb.Length)
+            {
+                return -1;
+            }
+
+            if ((ulong)intFbList.Value.IntFb[i].Data.Length < minSize)
+            {
+                if (!intFbList.Value.IntFb[i].Data.IsNull)
+                {
+                    allocator.Free(intFbList.Value.IntFb[i].Data);
+                }
+
+                // The data must be zeroed to fix a valgrind error from the C loop filter
+                // due to access uninitialized memory in frame border. It could be
+                // skipped if border were totally removed.
+                intFbList.Value.IntFb[i].Data = allocator.Allocate<byte>((int)minSize);
+                if (intFbList.Value.IntFb[i].Data.IsNull)
+                {
+                    return -1;
+                }
+            }
+
+            fb.Data = intFbList.Value.IntFb[i].Data;
+            intFbList.Value.IntFb[i].InUse = true;
+
+            // Set the frame buffer's private data to point at the internal frame buffer.
+            fb.Priv = new Ptr<InternalFrameBuffer>(ref intFbList.Value.IntFb[i]);
+            return 0;
+        }
+
+        public static int ReleaseFrameBuffer(Ptr<InternalFrameBufferList> cbPriv, ref VpxCodecFrameBuffer fb)
+        {
+            if (!fb.Priv.IsNull)
+            {
+                fb.Priv.Value.InUse = false;
+            }
+
+            return 0;
+        }
+    }
+}