Merge pull request #20299 from PJB3005/18-07-20-cs-editorconfig

Adds C# rule to .editorconfig.

.editorconfig

@@ -9,7 +9,7 @@ insert_final_newline = true
 [*.{cpp,hpp,c,h,mm}]
 trim_trailing_whitespace = true
 
-[*.py]
+[*.{py,cs}]
 indent_style = space
 indent_size = 4