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/CodeGen/Glsl/OperandManager.cs

@@ -13,7 +13,7 @@ namespace Ryujinx.Graphics.Shader.CodeGen.Glsl
     {
         private static readonly string[] StagePrefixes = new string[] { "cp", "vp", "tcp", "tep", "gp", "fp" };
 
-        private struct BuiltInAttribute
+        private readonly struct BuiltInAttribute
         {
             public string Name { get; }