Use a full EndpointRef on ComputedRoutes targets instead of just the ID

* Use a full EndpointRef on ComputedRoutes targets instead of just the ID

Today, the `ComputedRoutes` targets have the appropriate ID set for their `ServiceEndpoints` reference; however, the `MeshPort` and `RoutePort` are assumed to be that of the target when adding the endpoints reference in the sidecar's `ProxyStateTemplate`.

This is problematic when the target lives behind a `MeshGateway` and the `Mesh/RoutePort` used in the sidecar's `ProxyStateTemplate` should be that of the `MeshGateway` instead of the target.

Instead of assuming the `MeshPort` and `RoutePort` when building the `ProxyStateTemplate` for the sidecar, let's just add the full `EndpointRef` -- including the ID and the ports -- when hydrating the computed destinations.

* Make sure the UID from the existing ServiceEndpoints makes it onto ComputedRoutes

* Update test assertions

* Undo confusing whitespace change

* Remove one-line function wrapper

* Use plural name for endpoints ref

* Add constants for gateway name, kind and port names