Fix "Add Network" button on SavedAccessPoints page.

Fix merge conflict.

The old onSubmit was a no-op. It now correctly pipes onSubmit to
WifiManager#save() with the new WifiConfiguration. On successful save,
it displays the new network in the list, and on failure, it displays a
toast indicating that the save action failed. Adds a test for the
WifiDialog behaviors on this page.

Bug: 66177765
Test: make RunSettingsRoboTests, manual - tested with Wifi enabled and
disabled, and with networks that were visible and not.
Change-Id: I27446aa49bc9efaf1ea1d6c6158928b62ce01ba2