Implement NGC service (#5681)

* Implement NGC service

* Use raw byte arrays instead of string for _wordSeparators

* Silence IDE0230 for _wordSeparators

* Try to silence warning about _rangeValuesCount not being read on SparseSet

* Make AcType enum private

* Add abstract methods and one TODO that I forgot

* PR feedback

* More PR feedback

* More PR feedback

src/Ryujinx.Horizon/Sdk/Fs/FileHandle.cs

@@ -0,0 +1,13 @@
+
+namespace Ryujinx.Horizon.Sdk.Fs
+{
+    public readonly struct FileHandle
+    {
+        public object Value { get; }
+
+        public FileHandle(object value)
+        {
+            Value = value;
+        }
+    }
+}

src/Ryujinx.Horizon/Sdk/Fs/FsResult.cs

@@ -0,0 +1,13 @@
+using Ryujinx.Horizon.Common;
+
+namespace Ryujinx.Horizon.Sdk.Fs
+{
+    static class FsResult
+    {
+        private const int ModuleId = 2;
+
+        public static Result PathNotFound => new(ModuleId, 1);
+        public static Result PathAlreadyExists => new(ModuleId, 2);
+        public static Result TargetNotFound => new(ModuleId, 1002);
+    }
+}

src/Ryujinx.Horizon/Sdk/Fs/IFsClient.cs

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+using Ryujinx.Horizon.Common;
+using System;
+
+namespace Ryujinx.Horizon.Sdk.Fs
+{
+    public interface IFsClient
+    {
+        Result QueryMountSystemDataCacheSize(out long size, ulong dataId);
+        Result MountSystemData(string mountName, ulong dataId);
+        Result OpenFile(out FileHandle handle, string path, OpenMode openMode);
+        Result ReadFile(FileHandle handle, long offset, Span<byte> destination);
+        Result GetFileSize(out long size, FileHandle handle);
+        void CloseFile(FileHandle handle);
+        void Unmount(string mountName);
+    }
+}

src/Ryujinx.Horizon/Sdk/Fs/OpenMode.cs

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+using System;
+
+namespace Ryujinx.Horizon.Sdk.Fs
+{
+    [Flags]
+    public enum OpenMode
+    {
+        Read = 1,
+        Write = 2,
+        AllowAppend = 4,
+        ReadWrite = 3,
+        All = 7,
+    }
+}