[libtaskmanager] Fix incorrect URL comparison when writing back a new launcher order

When computing the delta between the visible and the last saved launcher
order state, following the reordering of launchers, the code was incorrectly
comparing resolved and unresolved (i.e., for config storage) launcher URLs.
This lead to an incorrect result and therefore pinned tasks jumping around
in the Task Manager applet.

BUG:426880
(cherry picked from commit fa00ca6a)