We bind to each available AutofillService, fetch the number of saved
passwords, then unbind and update the UI.
Each ServiceConnection is wired up to the controller's lifecycle so they
can be unbound when the lifecycle owner is destroyed.
Bug: 169455298
Test: manual - check value in the UI
Test: manual - no ServiceConnection leak, even when there's no response
Test: atest \
SettingsUnitTests:com.android.settings.applications.autofill.PasswordsPreferenceControllerTest
Change-Id: I7008e979e9292b99c8611010e49b3e738c82bfed
63fb2f10d5