QTextDocument: allow css border-style of table collapsed cell borders

8664ee610d added support for collapsed
borders but set the style to solid no matter what border-style defined.
Fix it by properly setting the desired border style.

Task-number: QTBUG-36152
Change-Id: Ie527511f831e7f62ab7064d4958b35ddbf1a9403
Pick-to: 5.12
Reviewed-by: Nils Jeisecke <nils.jeisecke@saltation.com>
Reviewed-by: Samuel Gaist <samuel.gaist@idiap.ch>

src/gui/text/qtextdocumentlayout.cpp

@@ -1616,7 +1616,7 @@ void drawCellBorder(const QTextDocumentLayoutPrivate *p, QPainter *painter,
     QBrush brush;
 
     if (edgeData.edgeClass != EdgeData::ClassExplicit && td->drawGrid) {
-        borderStyle = QTextFrameFormat::BorderStyle_Solid;
+        borderStyle = table->format().borderStyle();
         brush = table->format().borderBrush();
     }
     else {