tree-wide: stop using canonicalize_file_name(), use chase_symlinks() instead

Let's use chase_symlinks() everywhere, and stop using GNU
canonicalize_file_name() everywhere. For most cases this should not change
behaviour, however increase exposure of our function to get better tested. Most
importantly in a few cases (most notably nspawn) it can take the correct root
directory into account when chasing symlinks.

src/basic/path-util.h

@@ -66,8 +66,8 @@ static inline bool path_equal_ptr(const char *a, const char *b) {
         })
 
 int path_strv_make_absolute_cwd(char **l);
-char** path_strv_resolve(char **l, const char *prefix);
-char** path_strv_resolve_uniq(char **l, const char *prefix);
+char** path_strv_resolve(char **l, const char *root);
+char** path_strv_resolve_uniq(char **l, const char *root);
 
 int find_binary(const char *name, char **filename);