Move partial unmap handler to the native signal handler (#3437)

* Initial commit with a lot of testing stuff.

* Partial Unmap Cleanup Part 1

* Fix some minor issues, hopefully windows tests.

* Disable partial unmap tests on macos for now

Weird issue.

* Goodbye magic number

* Add COMPlus_EnableAlternateStackCheck for tests

`COMPlus_EnableAlternateStackCheck` is needed for NullReferenceException handling to work on linux after registering the signal handler, due to how dotnet registers its own signal handler.

* Address some feedback

* Force retry when memory is mapped in memory tracking

This case existed before, but returning `false` no longer retries, so it would crash immediately after unprotecting the memory... Now, we return `true` to deliberately retry.

This case existed before (was just broken by this change) and I don't really want to look into fixing the issue right now. Technically, this means that on guest code partial unmaps will retry _due to this_ rather than hitting the handler. I don't expect this to cause any issues.

This should fix random crashes in Xenoblade Chronicles 2.

* Use IsRangeMapped

* Suppress MockMemoryManager.UnmapEvent warning

This event is not signalled by the mock memory manager.

* Remove 4kb mapping

Ryujinx.Common/Memory/PartialUnmaps/ThreadLocalMap.cs

@@ -0,0 +1,92 @@
+using System.Runtime.InteropServices;
+using System.Threading;
+
+using static Ryujinx.Common.Memory.PartialUnmaps.PartialUnmapHelpers;
+
+namespace Ryujinx.Common.Memory.PartialUnmaps
+{
+    /// <summary>
+    /// A simple fixed size thread safe map that can be used from native code.
+    /// Integer thread IDs map to corresponding structs.
+    /// </summary>
+    /// <typeparam name="T">The value type for the map</typeparam>
+    [StructLayout(LayoutKind.Sequential, Pack = 1)]
+    public struct ThreadLocalMap<T> where T : unmanaged
+    {
+        public const int MapSize = 20;
+
+        public Array20<int> ThreadIds;
+        public Array20<T> Structs;
+
+        public static int ThreadIdsOffset;
+        public static int StructsOffset;
+
+        /// <summary>
+        /// Populates the field offsets for use when emitting native code.
+        /// </summary>
+        static ThreadLocalMap()
+        {
+            ThreadLocalMap<T> instance = new ThreadLocalMap<T>();
+
+            ThreadIdsOffset = OffsetOf(ref instance, ref instance.ThreadIds);
+            StructsOffset = OffsetOf(ref instance, ref instance.Structs);
+        }
+
+        /// <summary>
+        /// Gets the index of a given thread ID in the map, or reserves one.
+        /// When reserving a struct, its value is set to the given initial value.
+        /// Returns -1 when there is no space to reserve a new entry.
+        /// </summary>
+        /// <param name="threadId">Thread ID to use as a key</param>
+        /// <param name="initial">Initial value of the associated struct.</param>
+        /// <returns>The index of the entry, or -1 if none</returns>
+        public int GetOrReserve(int threadId, T initial)
+        {
+            // Try get a match first.
+
+            for (int i = 0; i < MapSize; i++)
+            {
+                int compare = Interlocked.CompareExchange(ref ThreadIds[i], threadId, threadId);
+
+                if (compare == threadId)
+                {
+                    return i;
+                }
+            }
+
+            // Try get a free entry. Since the id is assumed to be unique to this thread, we know it doesn't exist yet.
+
+            for (int i = 0; i < MapSize; i++)
+            {
+                int compare = Interlocked.CompareExchange(ref ThreadIds[i], threadId, 0);
+
+                if (compare == 0)
+                {
+                    Structs[i] = initial;
+                    return i;
+                }
+            }
+
+            return -1;
+        }
+
+        /// <summary>
+        /// Gets the struct value for a given map entry.
+        /// </summary>
+        /// <param name="index">Index of the entry</param>
+        /// <returns>A reference to the struct value</returns>
+        public ref T GetValue(int index)
+        {
+            return ref Structs[index];
+        }
+
+        /// <summary>
+        /// Releases an entry from the map.
+        /// </summary>
+        /// <param name="index">Index of the entry to release</param>
+        public void Release(int index)
+        {
+            Interlocked.Exchange(ref ThreadIds[index], 0);
+        }
+    }
+}