Fix class name lookup for single file mapping

[AntoineGautier]

When mapping a package to a file, the function searchpath from ./lib/util.js returns the package file path for any class defined in the package.
This function is used in lib/expressionEvaluation.js to retrieve the class definition for a given type specifier.
This will fail in case of single file mapping, typically used for type definitions in MBL.
This ticket will append the simple class name in case the file name returned by searchpath does not match the simple class name.