EndpointSlice is always enabled now, so make it non-optional in the
EndpointsAdapter, make all of the test cases pass an EndpointSlice
client, and remove the "EndpointSlices disabled"-specific tests.
By changing makeEndpointsArray() to return both an Endpoints and an
EndpointsSlice, the "initialObjects" and "expectCreate"/"expectUpdate"
fields of (almost) all of the existing unit tests are automatically
switched to be EndpointSlice-aware; instead of having an initial state
with just Endpoints (or nothing), and testing that just the Endpoints
is created/updated correctly, they now have an initial state with both
Endpoints and EndpointSlice (or nothing), and test that both objects
are created/updated correctly.
The handful of existing test cases that used inconsistent Endpoints
and EndpointSlice state have been modified to create the objects
separately.
91338c13df