Refactor EphemeralResolverService

* Change name to InstantAppResolverService
* Left old service in place to handle existing client
  [to be removed prior to O launch]
* When resolving phase II, return a list instead of a single item

Bug: 34763730
Test: Build and verify resolution occurs w/ legacy & new resolver service
Change-Id: Ieccaf91538bd91c04f4be4e35d8264619d7cd6d7