EXPERIMENTAL: Metal backend (#441)

This is not a continuation of the Metal backend; this is simply bringing
the branch up to date and merging it as-is behind an experiment.

---------

Co-authored-by: Isaac Marovitz <isaacryu@icloud.com>
Co-authored-by: Samuliak <samuliak77@gmail.com>
Co-authored-by: SamoZ256 <96914946+SamoZ256@users.noreply.github.com>
Co-authored-by: Isaac Marovitz <42140194+IsaacMarovitz@users.noreply.github.com>
Co-authored-by: riperiperi <rhy3756547@hotmail.com>
Co-authored-by: Gabriel A <gab.dark.100@gmail.com>

src/Ryujinx.Graphics.Metal/StateCache.cs

@@ -0,0 +1,42 @@
+using System;
+using System.Collections.Generic;
+using System.Runtime.Versioning;
+
+namespace Ryujinx.Graphics.Metal
+{
+    [SupportedOSPlatform("macos")]
+    abstract class StateCache<T, TDescriptor, THash> : IDisposable where T : IDisposable
+    {
+        private readonly Dictionary<THash, T> _cache = new();
+
+        protected abstract THash GetHash(TDescriptor descriptor);
+
+        protected abstract T CreateValue(TDescriptor descriptor);
+
+        public void Dispose()
+        {
+            foreach (T value in _cache.Values)
+            {
+                value.Dispose();
+            }
+
+            GC.SuppressFinalize(this);
+        }
+
+        public T GetOrCreate(TDescriptor descriptor)
+        {
+            var hash = GetHash(descriptor);
+            if (_cache.TryGetValue(hash, out T value))
+            {
+                return value;
+            }
+            else
+            {
+                var newValue = CreateValue(descriptor);
+                _cache.Add(hash, newValue);
+
+                return newValue;
+            }
+        }
+    }
+}