feat(editor): a join of ends side by side shifts the track with reverse curves over the whole gap

The reverse curves of a join start and end at the joined ends, with the
largest radius that fits, so a shift of the track spacing (4 -> 4.75 m
over 400 m) is one S instead of two curves with straights around them.
A straight or a single arc with a kink at its ends, though still under
the joints check, comes after the smooth curves among the variants; a
practically exact one stays first.

An element under 1 mm, like the straight left between the reverse
curves by the radius fit, no longer drops out of the pieces and leaves
a gap: the neighbouring piece takes it over.

editor/editorAlignment.hpp

@@ -232,6 +232,7 @@ struct join_result
 	double cant{0.0};
 	double transition{0.0};
 	double speed{0.0};
+	double kink{0.0};
 	int variants{0};
 	std::vector<std::string> warnings;
 	std::vector<std::string> radius_warnings;