util/OptionParser: move to cmdline/

This library will depend on libfmt, and libutil shouldn't depend on
any library.

test/run_convert.cxx

@@ -31,8 +31,8 @@
 #include "fs/NarrowPath.hxx"
 #include "io/FileDescriptor.hxx"
 #include "util/StaticFifoBuffer.hxx"
-#include "util/OptionDef.hxx"
-#include "util/OptionParser.hxx"
+#include "cmdline/OptionDef.hxx"
+#include "cmdline/OptionParser.hxx"
 #include "util/PrintException.hxx"
 #include "Log.hxx"
 #include "LogBackend.hxx"