This allows us to filter `IEndpointSelectorPolicy` instance based on
whether the apply to a given candidate set. This should allow us to
remove some HAXXX from MVC.
The idea here is the ESP becomes much more pay-for-play if you can
statically eliminate many of the cases where it would usually no op.
Adds logging for the most common things that can prevent an endpoint
from matching.
Note that we already have good logging in other parts of the system, the
stuff here completes the story by providing details at the debug level.
Ryan Nowak
James Newton-King