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.Gpu/Engine/Threed/StateUpdateTracker.cs

@@ -11,7 +11,7 @@ namespace Ryujinx.Graphics.Gpu.Engine.Threed
     /// <summary>
     /// State update callback entry, with the callback function and associated field names.
     /// </summary>
-    struct StateUpdateCallbackEntry
+    readonly struct StateUpdateCallbackEntry
     {
         /// <summary>
         /// Callback function, to be called if the register was written as the state needs to be updated.