create helper classes

DotNetSolutionTools.Core/Common/CsprojHelper.cs

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+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;
+    }
+}

DotNetSolutionTools.Core/Common/SlnHelper.cs

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+using Microsoft.Build.Construction;
+
+namespace DotNetSolutionTools.Core.Common;
+
+public static class SlnHelper
+{
+    public static SolutionFile? ParseSolutionFileFromPath(string solutionFilePath)
+    {
+        var solutionFile = SolutionFile.Parse(solutionFilePath);
+
+        return solutionFile;
+    }
+
+    public static List<ProjectRootElement> GetCSharpProjectObjectsFromSolutionFile(SolutionFile solutionFile)
+    {
+        var projectList = solutionFile
+            .ProjectsByGuid.Where(x => x.Value.ProjectType == SolutionProjectType.KnownToBeMSBuildFormat)
+            .Select(s => ProjectRootElement.Open(s.Value.AbsolutePath))
+            .ToList();
+
+        return projectList;
+    }
+}