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

ARMeilleure/Translation/Translator.cs

@@ -293,7 +293,7 @@ namespace ARMeilleure.Translation
             }
         }
 
-        private struct Range
+        private readonly struct Range
         {
             public ulong Start { get; }
             public ulong End { get; }