Make structs readonly when applicable (#4002)

* Make all structs readonly when applicable. It should reduce amount of needless defensive copies

* Make structs with trivial boilerplate equality code record structs

* Remove unnecessary readonly modifiers from TextureCreateInfo

* Make BitMap structs readonly too

Ryujinx.Graphics.Shader/Decoders/Block.cs

@@ -17,7 +17,7 @@ namespace Ryujinx.Graphics.Shader.Decoders
         }
     }
 
-    struct SyncTarget
+    readonly struct SyncTarget
     {
         public PushOpInfo PushOpInfo { get; }
         public int PushOpId { get; }