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/Translation/Ssa.cs

@@ -108,7 +108,7 @@ namespace Ryujinx.Graphics.Shader.Translation
             }
         }
 
-        private struct Definition
+        private readonly struct Definition
         {
             public BasicBlock Block { get; }
             public Operand    Local { get; }