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/GpuChannelComputeState.cs

@@ -3,7 +3,7 @@ namespace Ryujinx.Graphics.Gpu.Shader
     /// <summary>
     /// State used by the <see cref="GpuAccessor"/>.
     /// </summary>
-    struct GpuChannelComputeState
+    readonly struct GpuChannelComputeState
     {
         // New fields should be added to the end of the struct to keep disk shader cache compatibility.