fs/Path: rename to AllocatedPath

The new class Path only holds a string pointer without being
responsible for allocation/deallocation.  The FileSystem.hxx library
accepts Path arguments instead of AllocatedPath, to avoid forcing
callers to allocate another string object.

src/TextFile.cxx

@@ -27,7 +27,7 @@
 #include <assert.h>
 #include <string.h>
 
-TextFile::TextFile(const Path &path_fs)
+TextFile::TextFile(Path path_fs)
 	:file(FOpen(path_fs, FOpenMode::ReadText)),
 	 buffer(g_string_sized_new(step)) {}