[CS] Support "instant failure" from factories

Add a mechanism by which a factory can declare "instant failure" for
a request - which would result in it getting an OnUnavailable()
(even without a timeout).

Factories may only do this iff:
1. They know they are the only factory which may fulfill this
   request (common for transport-specific requests).
2. The know that the request can definitely not be
   fulfilled at any point in the future.

Bug: 31382922
Test: atest ConnectivityServiceTest
Merged-In: I9bce0f4d85fa8cad7f8a9998819f945b778c5ac5
Change-Id: I9bce0f4d85fa8cad7f8a9998819f945b778c5ac5