fdo#38215: merge consecutive border lines:
fdo#38215: merge consecutive border lines:

This re-implements the merging that was done by SwLineRects::AddLineRect,
SwLineRect::MakeUnion with the drawing layer border lines.
This is used to merge borders of paragraphs and of tables that have the
"separating" border-model, which fixes both the tiny dividing gaps
between successive borders in the second bugdoc and the weird subtly
differently rendered successive borders in the first bugdoc.
(regression from 0f0896c26fb260d1bbf31d7a886df3f61837f0f2)

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core