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/Shader/DiskCache/GuestCodeAndCbData.cs

@@ -3,7 +3,7 @@ namespace Ryujinx.Graphics.Gpu.Shader.DiskCache
     /// <summary>
     /// Guest shader code and constant buffer data accessed by the shader.
     /// </summary>
-    struct GuestCodeAndCbData
+    readonly struct GuestCodeAndCbData
     {
         /// <summary>
         /// Maxwell binary shader code.