Prepare Flax.Build project for .NET 7

Add .NET SDK project generator and upgrade Flax.Build project files

Source/Tools/Flax.Build/Platforms/Android/AndroidToolchain.cs

@@ -5,6 +5,7 @@ using System.Collections.Generic;
 using System.IO;
 using Flax.Build.Graph;
 using Flax.Build.NativeCpp;
+using Task = Flax.Build.Graph.Task;
 
 namespace Flax.Build
 {

Source/Tools/Flax.Build/Platforms/Linux/LinuxToolchain.cs

@@ -4,6 +4,7 @@ using System.Collections.Generic;
 using System.IO;
 using Flax.Build.Graph;
 using Flax.Build.NativeCpp;
+using Task = Flax.Build.Graph.Task;
 
 namespace Flax.Build.Platforms
 {

Source/Tools/Flax.Build/Platforms/Mac/MacToolchain.cs

@@ -5,6 +5,7 @@ using System.IO;
 using System.Collections.Generic;
 using Flax.Build.Graph;
 using Flax.Build.NativeCpp;
+using Task = Flax.Build.Graph.Task;
 
 namespace Flax.Build
 {

Source/Tools/Flax.Build/Platforms/Unix/UnixPlatform.cs

@@ -54,7 +54,7 @@ namespace Flax.Build.Platforms
                 StartInfo =
                 {
                     FileName = "/bin/sh",
-                    Arguments = string.Format("-c 'which {0}'", name),
+                    ArgumentList = { "-c", $"which {name}" },
                     UseShellExecute = false,
                     CreateNoWindow = true,
                     RedirectStandardOutput = true,

Source/Tools/Flax.Build/Platforms/Unix/UnixToolchain.cs

@@ -7,6 +7,7 @@ using System.IO;
 using System.Text.RegularExpressions;
 using Flax.Build.Graph;
 using Flax.Build.NativeCpp;
+using Task = Flax.Build.Graph.Task;
 
 namespace Flax.Build.Platforms
 {

Source/Tools/Flax.Build/Platforms/Windows/WindowsToolchainBase.cs

@@ -9,6 +9,7 @@ using System.Xml;
 using Flax.Build.Graph;
 using Flax.Build.NativeCpp;
 using Flax.Build.Projects.VisualStudio;
+using Task = Flax.Build.Graph.Task;
 
 // ReSharper disable InconsistentNaming