LOHS: use Executor and AIDL interface internally

This enables us to use Executor in new external APIs (as recommended).
This also migrates the LOHS callbacks to an AIDL interface, which
results in cleaner and type-safe code, and allows us to use Executor
without an extra layer of indirection.

Test: atest android.net.wifi.WifiManagerTest LocalOnlyHotspotRequestInfoTest WifiServiceImplTest android.net.wifi.cts.WifiManagerTest
Bug: 132705022
Change-Id: I621062fd3865ca048c022c7ad3520ae4694fc0df