Implemented solution for #570 (deep Edges::extents)

While doing this, it was discovered that the problem also
persists for EdgePairs and Texts.

In order to provide a more generic solution, some refactoring
was applied.

testdata/drc/drcSimpleTests_16.drc

@@ -0,0 +1,16 @@
+
+source($drc_test_source)
+target($drc_test_target)
+
+deep
+
+input(2,0).output(2, 0)
+input(3,0).output(3, 0)
+input(4,0).output(4, 0)
+input(9,0).output(9, 0)
+
+input(2,0).edges.extents(10.nm, 10.nm).output(102, 0)
+input(3,0).edges.extents(10.nm, 20.nm).output(103, 0)
+input(4,0).edges.extents(20.nm, 10.nm).output(104, 0)
+input(9,0).edges.extents(20.nm).output(109, 0)
+