Add nethost module and EngineConfiguration for .NET runtime

Source/ThirdParty/nethost/FlaxEngine.CSharp.runtimeconfig.json

@@ -0,0 +1,9 @@
+{
+  "runtimeOptions": {
+    "tfm": "net7.0",
+    "framework": {
+      "name": "Microsoft.NETCore.App",
+      "version": "7.0.0-rc.2.22472.3"
+    }
+  }
+}

Source/ThirdParty/nethost/LICENSE.TXT

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+The MIT License (MIT)
+
+Copyright (c) .NET Foundation and Contributors
+
+All rights reserved.
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

Source/ThirdParty/nethost/nethost.Build.cs

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+// Copyright (c) 2012-2022 Wojciech Figat. All rights reserved.
+
+using System.Collections.Generic;
+using System.IO;
+using System;
+using Flax.Build;
+using Flax.Build.NativeCpp;
+using Flax.Build.Platforms;
+using Microsoft.Win32;
+using System.Linq;
+
+/// <summary>
+/// Module for nethost (.NET runtime host library)
+/// </summary>
+public class nethost : ThirdPartyModule
+{
+    /// <inheritdoc />
+    public override void Init()
+    {
+        base.Init();
+
+        LicenseType = LicenseTypes.MIT;
+        LicenseFilePath = "LICENSE.TXT";
+
+        // Merge third-party modules into engine binary
+        BinaryModuleName = "FlaxEngine";
+    }
+
+    /// <inheritdoc />
+    private static Version ParseVersion(string version)
+    {
+        // Give precedence to final releases over release candidate / beta releases
+        int rev = 9999;
+        if (version.Contains("-")) // e.g. 7.0.0-rc.2.22472.3
+        {
+            version = version.Substring(0, version.IndexOf("-"));
+            rev = 0;
+        }
+        Version ver = new Version(version);
+        return new Version(ver.Major, ver.Minor, ver.Build, rev);
+    }
+
+    /// <inheritdoc />
+    public override void Setup(BuildOptions options)
+    {
+        base.Setup(options);
+
+        options.SourceFiles.Clear();
+
+        string appHostRuntimePath;
+        if (options.Platform.Target == TargetPlatform.Windows)
+        {
+            // NOTE: nethost is bundled with SDK, not runtime. Should C# scripting have a hard requirement for SDK to be installed?
+
+            string arch = "x64"; //options.Architecture == TargetArchitecture.x64 ? "x64" : "x86";
+
+            using RegistryKey baseKey = RegistryKey.OpenBaseKey(RegistryHive.LocalMachine, RegistryView.Registry64);
+
+            using RegistryKey hostKey = baseKey.OpenSubKey(@$"SOFTWARE\dotnet\Setup\InstalledVersions\{arch}\sharedhost");
+            string dotnetPath = (string)hostKey.GetValue("Path");
+
+            using RegistryKey runtimeKey = baseKey.OpenSubKey(@$"SOFTWARE\WOW6432Node\dotnet\Setup\InstalledVersions\{arch}\sharedfx\Microsoft.NETCore.App");
+            string[] versions = runtimeKey.GetValueNames();
+
+            string dotnetVersion = versions.OrderByDescending(x => ParseVersion(x)).FirstOrDefault();
+
+            if (string.IsNullOrEmpty(dotnetPath))
+                dotnetPath = Environment.GetEnvironmentVariable("DOTNET_ROOT");
+
+            if (string.IsNullOrEmpty(dotnetPath) || string.IsNullOrEmpty(dotnetVersion))
+                throw new Exception("Failed to find dotnet installation");
+
+            int majorVersion = int.Parse(dotnetVersion.Substring(0, dotnetVersion.IndexOf(".")));
+            if (majorVersion < 7)
+                throw new Exception($"Unsupported dotnet version found, minimum version required is .NET 7 (found {dotnetVersion})");
+
+            appHostRuntimePath = String.Format("{0}packs\\Microsoft.NETCore.App.Host.win-{1}\\{2}\\runtimes\\win-{1}\\native", dotnetPath, arch, dotnetVersion);
+            options.OutputFiles.Add(Path.Combine(appHostRuntimePath, "nethost.lib"));
+            options.DependencyFiles.Add(Path.Combine(appHostRuntimePath, "nethost.dll"));
+            options.PublicIncludePaths.Add(appHostRuntimePath);
+        }
+        else
+        {
+            // /etc/dotnet/install_location
+            throw new InvalidPlatformException(options.Platform.Target);
+        }
+
+        options.PublicIncludePaths.Add(appHostRuntimePath);
+        options.ScriptingAPI.Defines.Add("USE_NETCORE");
+        options.DependencyFiles.Add(Path.Combine(FolderPath, "FlaxEngine.CSharp.runtimeconfig.json"));
+    }
+}