Make edge metrics strongly typed (#6421)

This change takes the existing typedefs for weight, duration and
distance, and makes them proper types, using the existing Alias
functionality.

Primarily this is to prevent bugs where the metrics are switched,
but it also adds additional documentation. For example, it now
makes it clear (despite the naming of variables) that most of the
trip algorithm is running on the duration metric.

I've not made any changes to the casts performed between metrics
and numeric types, they now just more explicit.

src/extractor/extractor.cpp

@@ -668,7 +668,7 @@ void Extractor::FindComponents(unsigned number_of_edge_based_nodes,
 
     for (const auto &edge : input_edge_list)
     {
-        BOOST_ASSERT_MSG(static_cast<unsigned int>(std::max(edge.data.weight, 1)) > 0,
+        BOOST_ASSERT_MSG((std::max(edge.data.weight, EdgeWeight{1})) > EdgeWeight{0},
                          "edge distance < 1");
         BOOST_ASSERT(edge.source < number_of_edge_based_nodes);
         BOOST_ASSERT(edge.target < number_of_edge_based_nodes);