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.