Add dotnet format to tidy.py

BuildTools/tidy.py

@@ -1,6 +1,6 @@
 #!/usr/bin/env python
 
-import os, sys
+import os, sys, subprocess
 
 def check(filename):
 	ok = True
@@ -16,7 +16,8 @@ def main():
 	dirs_to_check = (
 		os.path.join(root_dir, subdir)
 		for subdir in ('ICSharpCode.Decompiler', 'ICSharpCode.Decompiler.Tests', 'ILSpy', 'ILSpy.BamlDecompiler'))
-	ok = True
+	format_result = subprocess.call(['dotnet', 'format', '--check', '--verbosity', 'detailed', os.path.join(root_dir, 'ILSpy.sln')])
+	ok = format_result == 0
 	for dir in dirs_to_check:
 		for root, dirs, files in os.walk(dir):
 			if '\\obj\\' in root: