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.Device/RwCallback.cs

@@ -2,7 +2,7 @@
 
 namespace Ryujinx.Graphics.Device
 {
-    public struct RwCallback
+    public readonly struct RwCallback
     {
         public Action<int> Write { get; }
         public Func<int> Read { get; }