Refactor AccessPointPreference

Make it extend from TwoTargetPreference because AccessPointPreference
do have the second target in the right part(secure icon).

Following cl will create ConnectedAccessPointPreference and make it
extend from AccessPointPreference, so we could reuse bunch of methods.

Bug: 68807544
Test: Existing tests pass.
Change-Id: Ie902366a4d0dbbe910957eb3658ea8fe7ad9c5da