Currently there is an edge-case in the turn restriction implementation,
such that routes can not be found if the target input location snaps
to a way used in a (multi) via restriction.
With the addition of snapping input locations to multiple ways, we
can now also snap to the "duplicate" edges created for the restriction graph,
thereby fixing the problem.
This is achieved by adding the duplicate restriction edges to the
geospatial search RTree.
This does open up the possibility of multiple paths representing exactly
the same route - one using the original edge as a source, the other
using the duplicate restriction graph edge as source. This is fine,
as both edges are represented by the same geometry, so will generate
the same result.
Currently OSRM only supports turn restrictions with a single via-node or one
via-way. OSM allows for multiple via-ways to represent longer and more
complex restrictions.
This PR extends the use of duplicate nodes for representng via-way turn
restrictions to also support multi via-way restrictions. Effectively, this
increases the edge-based graph size by the number of edges in multi via-way
restrictions. However, given the low number of these restrictions it
has little effect on total graph size.
In addition, we add a new step in the extraction phase that constructs
a restriction graph to support more complex relationships between restrictions,
such as nested restrictions and overlapping restrictions.
