tests: added test if CP1257-UTF8-CP1257 is lossless

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@42028 4005530d-fff6-0310-9dd1-cebe43e6787f
lazutils: made codepage conversion 852,874,1257,1258 to UTF8 and back is lossless

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@42029 4005530d-fff6-0310-9dd1-cebe43e6787f