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.Vic/Image/Surface.cs

@@ -3,7 +3,7 @@ using System.Runtime.CompilerServices;
 
 namespace Ryujinx.Graphics.Vic.Image
 {
-    struct Surface : IDisposable
+    readonly struct Surface : IDisposable
     {
         private readonly int _bufferIndex;
 

Ryujinx.Graphics.Vic/Rectangle.cs

@@ -1,6 +1,6 @@
 namespace Ryujinx.Graphics.Vic
 {
-    struct Rectangle
+    readonly struct Rectangle
     {
         public readonly int X;
         public readonly int Y;

Ryujinx.Graphics.Vic/ResourceManager.cs

@@ -3,7 +3,7 @@ using Ryujinx.Graphics.Vic.Image;
 
 namespace Ryujinx.Graphics.Vic
 {
-    struct ResourceManager
+    readonly struct ResourceManager
     {
         public MemoryManager Gmm { get; }
         public BufferPool<Pixel> SurfacePool { get; }