LazUtils: Fix ExpandFileNameUTF8 for directories with Unicode characters outside
current codepage on Windows.
Also do not remove trailing and leading spaces, it is inconsistent with
SysUtils.ExpandFileName.
Start splitting implementation in general, unix and windows specific includefiles.


git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@40842 4005530d-fff6-0310-9dd1-cebe43e6787f