Vulkan: Fix MoltenVK flickering (#5612)

#5576 changed where the position was declared, but forgot to add the Invariant declaration to position when the ReducedPrecision flag was enabled. This was causing weird graphical bugs in a bunch of games, mostly to do with mismatching depth between multiple draws of the same geometry.

Maybe the attempt to add it to Position in DeclareInputOrOutput can be removed now, assuming that path is never used.

src/Ryujinx.Graphics.Gpu/Shader/DiskCache/DiskCacheHostStorage.cs

@@ -22,7 +22,7 @@ namespace Ryujinx.Graphics.Gpu.Shader.DiskCache
         private const ushort FileFormatVersionMajor = 1;
         private const ushort FileFormatVersionMinor = 2;
         private const uint FileFormatVersionPacked = ((uint)FileFormatVersionMajor << 16) | FileFormatVersionMinor;
-        private const uint CodeGenVersion = 5540;
+        private const uint CodeGenVersion = 5609;
 
         private const string SharedTocFileName = "shared.toc";
         private const string SharedDataFileName = "shared.data";

src/Ryujinx.Graphics.Shader/CodeGen/Spirv/Declarations.cs

@@ -434,6 +434,11 @@ namespace Ryujinx.Graphics.Shader.CodeGen.Spirv
 
             context.Decorate(perVertexStructType, Decoration.Block);
 
+            if (context.HostCapabilities.ReducedPrecision)
+            {
+                context.MemberDecorate(perVertexStructType, 0, Decoration.Invariant);
+            }
+
             context.MemberDecorate(perVertexStructType, 0, Decoration.BuiltIn, (LiteralInteger)BuiltIn.Position);
             context.MemberDecorate(perVertexStructType, 1, Decoration.BuiltIn, (LiteralInteger)BuiltIn.PointSize);
             context.MemberDecorate(perVertexStructType, 2, Decoration.BuiltIn, (LiteralInteger)BuiltIn.ClipDistance);