Refactor GNSS listeners

Gnss listeners currently simply ignore requests that are not made in the
foreground or with appropriate permissions, even though these are
transitory attributes. In addition, some gnss listener use appops APIs
incorrectly. The RemoteListenerHelper pattern is not great either, and
makes it extremely difficult to write clear code, as well as duplicates
much of the functionality provided by AbstractListenerManager on the
client side. This CL unifies logic for multiplexing listeners so it can
be used across both the client and server side, and updates all GNSS
listeners to use the new model, which properly respects foreground,
appops, permissions, gnss enablement, and capabilities.

Test: presubmits + manual
Change-Id: I8f158e860e10c3ed43b246f6f3687169ac134343