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/ShaderCodeAccessor.cs

@@ -7,7 +7,7 @@ namespace Ryujinx.Graphics.Gpu.Shader
     /// <summary>
     /// Shader code accessor.
     /// </summary>
-    struct ShaderCodeAccessor : IDataAccessor
+    readonly struct ShaderCodeAccessor : IDataAccessor
     {
         private readonly MemoryManager _memoryManager;
         private readonly ulong _baseAddress;