create helper classes

DotNetSolutionTools.Core/Common/CsprojHelper.cs

@@ -0,0 +1,24 @@
+using Microsoft.Build.Construction;
+
+namespace DotNetSolutionTools.Core.Common;
+
+public static class CsprojHelper
+{
+    public static string[] RetrieveAllCSharpProjectFullPathsFromFolder(string solutionFolderPath)
+    {
+        // if solutionFolderPath does not end with a slash, add one
+        if (solutionFolderPath[^1] != Path.DirectorySeparatorChar)
+        {
+            solutionFolderPath += Path.DirectorySeparatorChar;
+        }
+        var csprojList = Directory.GetFiles(solutionFolderPath, "*.csproj", SearchOption.AllDirectories);
+        return csprojList;
+    }
+
+    public static string[] RetrieveAllCSharpProjectFullPathsFromSolution(SolutionFile solution)
+    {
+        var result = SlnHelper.GetCSharpProjectObjectsFromSolutionFile(solution);
+        var csprojList = result.Select(x => x.FullPath).ToArray();
+        return csprojList;
+    }
+}