SettingsLib: wifi: encapsulate Passpoint configuration in AccessPoint

The configurations that are managed by "Saved Networks" page are
centered around the abstraction of AccessPoint.  Since we will
need to manage Passpoint configuration in the "Saved Networks"
(for configuration removal), encapsulate necessary information
in an AccessPoint for a Passpoint configuration.

Bug: 34207710
Test: manual test
Test: runtest --path
      frameworks/base/packages/SettingsLib/tests/integ/src/com/android/settingslib/wifi/AccessPointTest.java
Change-Id: Ide556f5ec6c4ef9e1f82016efe17dc9860f298de