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/Cache/CacheMemoryAllocator.cs

@@ -6,7 +6,7 @@ namespace ARMeilleure.Translation.Cache
 {
     class CacheMemoryAllocator
     {
-        private struct MemoryBlock : IComparable<MemoryBlock>
+        private readonly struct MemoryBlock : IComparable<MemoryBlock>
         {
             public int Offset { get; }
             public int Size { get; }