The property infos are already sorted by name. As nm_setting_enumerate_values()
now uses that information, in most cases there is nothing to sort.

The only instance is NMSettingConnection, which has a different
sort-order. At least for some purposes, not all:

  - nm_setting_enumerate_values(), obviously.

  - nm_setting_enumerate_values() is called by keyfile writer. That
    means, keyfile writer will persist properties in a sorted way.

Cache the property list with alternative sorting also in the
setting-meta data, instead of calculating it each time.

Beside caching the information, this has the additional benefit that
this kind of sorting is now directly available, without calling
nm_setting_enumerate_values(). Meaning, we can implement keyfile writer
without using nm_setting_enumerate_values().