Remove CH from GraphHopperStorage, allow delta import of CHs

[easbar]

Fixes #2388 and #2453.

Our current API to create CH graphs is this:

// encoding manager
FlagEncoder encoder = new CarFlagEncoder();
EncodingManager encodingManager = EncodingManager.create(encoder);
// before we even create the base graph we have to setup the CH graphs and corresponding Weightings
Weighting fastestWeighting = new FastestWeighting(encoder);
CHConfig chConfig = CHConfig.nodeBased("car", weighting);
GraphHopperStorage ghStorage = new GraphBuilder(encodingManager).addCHConfig(chConfig).create();
// run CH preparation
PrepareContractionHierarchies pch = PrepareContractionHierarchies.fromGraphHopperStorage(ghStorage, chConfig);
pch.doWork();
// get the resulting (now no longer empty) CH graph from GHStorage
RoutingCHGraph chGraph = ghStorage.getRoutingCHGraph("car");

with the present PR this becomes:

// encoding manager
FlagEncoder encoder = new CarFlagEncoder();
EncodingManager encodingManager = EncodingManager.create(encoder);
// create the base graph (not related to CH at all)
GraphHopperStorage ghStorage = new GraphBuilder(encodingManager).create();
ghStorage.freeze(); // once all edges were added to the base graph it is finished and we freeze it
// now we can add CHs on top of our base graph 
Weighting fastestWeighting = new FastestWeighting(encoder);
CHConfig chConfig = CHConfig.nodeBased("car", weighting);
PrepareContractionHierarchies pch = PrepareContractionHierarchies.fromGraphHopperStorage(ghStorage, chConfig);
PrepareContractionHierarchies.Result result = pch.doWork();
// ... the result of the preparation is the CHStorage, i.e. basically the CH levels and created shortcuts 
CHStorage chStorage = result.getCHStorage();
// we can obtain a CH graph from this:
RoutingCHGraph chGraph = ghStorage.createCHGraph(chStorage, chConfig);

// instead of using `PrepareContractionHierarchies` to build a CH we can also obtain a `CHStorage` using:
ghStorage.createCHStorage(chConfig);

I think this is a big improvement, because we no longer need to setup CHs even before the base graph was built. With this PR and some recent commits it was easy to implement CH delta imports (#2453). The base graph is also no longer coupled to CH.

I'm still not entirely happy with this API, because we still need to call ghStorage.createCHStorage/Graph to create the CH structures. This is because CHStorage depends on the number of nodes of the frozen base graph and RoutingCHGraph needs a reference to the BaseGraph, which is private and only visible for GraphHopperStorage. Long-term I actually think we should remove GraphHopperStorage entirely and make BaseGraph public instead, but I'd like to do this in another PR.

[easbar]

So far we only called ghStorage.close() here which 'closed' the base graph and the CH graphs, but not LM! Now we explicitly close CH and LM.