Add reference counted resources to IpSecService

This patch adds (but does not enable the usage of) RefcountedResource
objects to IpSecService, with tests to ensure correct function. This is
patch 1 of a series of patches to refactor the resource management
systems in IpSecService.

RefcountedResource objects allow for management of acyclical dependency
trees, ensuring eventual cleanup when resources are no longer used. This
cleanup may be triggered by binder death or by explicit user action.

Bug: 63409385
Test: New tests written in IpSecServiceRefcountedResourceTest,
explicitly testing the RefcountedResource class

Change-Id: Ib5be7482b2ef5f1c8dec9be68f15e90d8b3aba6d