Fix IDEA plugin behavior with classes in library sources

In case when some class was contained in sources of some library (in addition
to classes of some library) we incorrectly assumed that its ModuleInfo is
LibrarySourceInfo of that library, because we checked if the file was in
library sources first. Now we check if the file is in library _classes_ first,
and then sources

 #KT-5695 Fixed
KT-5697 Duplicate Unit type
 #KT-5697 Fixed