Fix line annotation arrows for usage in dimensioning

By combining leader lines with arrow/slash endings, one can use
AnnotLine for dimensioning (e.g. see Line Annotation key IT =
LineDimension in PDF reference). Current drawing instructions didn't
consider this use case. The combination of leader line with ROpenArrow,
RClosedArrow and Slash looked poor because arrows were shifted to the
inside of the leader strokes. Additionally the main segment was not
shortened correctly for some arrow types.

This fixes the mentioned issues for AnnotLine and AnnotPolygon.
6 jobs for bugfix/spurious_lineending in 4 minutes and 46 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #373267
build

00:04:46

passed #373272
build_android

00:01:13

passed #373268
build_clang_libcpp

00:02:41

passed #373271
build_clazy

00:03:27

passed #373270
build_mingw64_fedora

00:04:32

passed #373269
build_ubuntu_16_04

00:02:05