Fix launch issue when GodotProjectDir not same as SolutionDir

If the Solution for a Godot project is not the same as the project directory the extension will
fail to launch the debug target with a MessageBox showing 'No Godot editor instance connected'.

The reason is that the extension takes SolutionDir as the Godot project dir. While this hold true for
simple default Godot projects this must not be the case. In complex projects developers may
restructure their projects into a alternative structure, where the solution may be at another location.

The *.csproj file has the MSBuild property 'GodotProjectDir'. Now the value of this property is fetched
and will be used as the project dir.

Note: Godot itself has some issues with projects varying to the default project. To fix this godot issues,
modifications in the GodotSDK MSBuild props file have to be done.

Author: paiden

GodotAddinVS/GodotAddinVS.csproj

@@ -71,8 +71,10 @@
     </None>
   </ItemGroup>
   <ItemGroup>
+    <Reference Include="Microsoft.Build" />
     <Reference Include="Microsoft.CSharp" />
     <Reference Include="System" />
+    <Reference Include="System.Xml" />
   </ItemGroup>
   <ItemGroup>
     <PackageReference Include="Clide" Version="4.1.1" ExcludeAssets="runtime" />

GodotAddinVS/GodotSolutionEventsListener.cs

@@ -8,6 +8,7 @@
 using GodotAddinVS.GodotMessaging;
 using GodotTools.IdeMessaging;
 using GodotTools.IdeMessaging.Requests;
+using Microsoft.VisualStudio;
 using Microsoft.VisualStudio.Shell;
 using Microsoft.VisualStudio.Shell.Interop;
 
@@ -85,7 +86,7 @@ public override int OnAfterOpenProject(IVsHierarchy hierarchy, int added)
                 if (_registered)
                     return 0;
 
-                _godotProjectDir = SolutionDir;
+                _godotProjectDir = EvalGodotProjectDir(hierarchy);
 
                 DebuggerEvents = ServiceProvider.GetService<DTE>().Events.DebuggerEvents;
                 DebuggerEvents.OnEnterDesignMode += DebuggerEvents_OnEnterDesignMode;
@@ -162,5 +163,38 @@ private void Close()
                 DebuggerEvents = null;
             }
         }
+
+        private string EvalGodotProjectDir(IVsHierarchy hierarchy)
+        {
+            try
+            {
+                ThreadHelper.ThrowIfNotOnUIThread();
+                var dteProject = GetDTEProject(hierarchy);
+                if (dteProject == null)
+                {
+                    return SolutionDir;
+                }
+
+                var evalProj = new Microsoft.Build.Evaluation.Project(dteProject.FullName);
+                var evaluated = evalProj.GetPropertyValue("GodotProjectDir");
+                return string.IsNullOrWhiteSpace(evaluated) ? SolutionDir : evaluated;
+            }
+            catch
+            {
+                return SolutionDir;
+            }
+        }
+
+        private static EnvDTE.Project GetDTEProject(IVsHierarchy hierarchy)
+        {
+            ThreadHelper.ThrowIfNotOnUIThread();
+
+            var itemid = VSConstants.VSITEMID_ROOT;
+
+            object objProj;
+            hierarchy.GetProperty(itemid, (int)__VSHPROPID.VSHPROPID_ExtObject, out objProj);
+
+            return objProj as EnvDTE.Project;
+        }
     }
 }