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/Memory/BufferBounds.cs

@@ -5,7 +5,7 @@ namespace Ryujinx.Graphics.Gpu.Memory
     /// <summary>
     /// Memory range used for buffers.
     /// </summary>
-    struct BufferBounds
+    readonly struct BufferBounds
     {
         /// <summary>
         /// Region virtual address.

Ryujinx.Graphics.Gpu/Memory/BufferTextureBinding.cs

@@ -7,7 +7,7 @@ namespace Ryujinx.Graphics.Gpu.Memory
     /// <summary>
     /// A buffer binding to apply to a buffer texture.
     /// </summary>
-    struct BufferTextureBinding
+    readonly struct BufferTextureBinding
     {
         /// <summary>
         /// Shader stage accessing the texture.

Ryujinx.Graphics.Gpu/Memory/CounterCache.cs

@@ -8,7 +8,7 @@ namespace Ryujinx.Graphics.Gpu.Memory
     /// </summary>
     class CounterCache
     {
-        private struct CounterEntry
+        private readonly struct CounterEntry
         {
             public ulong Address { get; }
             public ICounterEvent Event { get; }