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.GAL/ProgramPipelineState.cs

@@ -6,7 +6,7 @@ namespace Ryujinx.Graphics.GAL
     /// <summary>
     /// Descriptor for a pipeline buffer binding.
     /// </summary>
-    public struct BufferPipelineDescriptor
+    public readonly struct BufferPipelineDescriptor
     {
         public bool Enable { get; }
         public int Stride { get; }