Added methods and flags to check what level of funcionality
the service supports.
Added flags to enable instant tether and nearby Wi-Fi. The flags
will be enabled in an overlay file based on the level of UI
support by the OEM. The service checks the flags and provides
an API to allow the API's client to decide what level
of functionality to provide.
Also fixed the naming of flags.

Bug: 271934662
Test: atest SharedConnectivityServiceTest
Change-Id: Ifba6b73904862dfdc58741856e8b940ae6d6634b