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.Horizon.Generators/Kernel/SyscallGenerator.cs

@@ -40,7 +40,7 @@ namespace Ryujinx.Horizon.Generators.Kernel
             $"{TypeKernelResultName}.InvalidState"
         };
 
-        private struct OutParameter
+        private readonly struct OutParameter
         {
             public readonly string Identifier;
             public readonly bool NeedsSplit;
@@ -104,7 +104,7 @@ namespace Ryujinx.Horizon.Generators.Kernel
             }
         }
 
-        private struct SyscallIdAndName : IComparable<SyscallIdAndName>
+        private readonly struct SyscallIdAndName : IComparable<SyscallIdAndName>
         {
             public readonly int Id;
             public readonly string Name;